Restructure into src/tests and add build foundation (M0)

Moves the scaffold to src/DodoSSH.Api and establishes the repo conventions the rest
of the milestones build on.

Structure:
- src/{Contracts,Crypto,Domain,Infrastructure,Api}, tests/{Contracts,Crypto,Domain}.Tests
- DodoSSH.slnx rewritten with src/ and tests/ solution folders

Build:
- Directory.Build.props centralises TFM, nullable, deterministic builds and
  TreatWarningsAsErrors; Directory.Packages.props pins every version centrally
- packages.lock.json committed so CI restores in locked mode
- NuGet.config clears machine-level sources, which both fixes NU1507 under central
  package management and makes restore reproducible off this machine
- Microsoft.OpenApi pinned to 2.11.0: ASP.NET Core 10.0.10 resolves 2.0.0, which is
  covered by GHSA-v5pm-xwqc-g5wc (high, patched in 2.7.5)

Analyzers:
- AnalysisLevel is Recommended, not All. With warnings-as-errors, All turns opinionated
  naming rules into build breaks and trains people to blanket-suppress.
- BannedSymbols.txt bans DateTime.UtcNow (TimeProvider), Guid.NewGuid (CreateVersion7),
  sync-over-async, MD5/SHA1, PBKDF2 and SecureString
- CA1711/CA1724 disabled: both are .NET Framework CAS-era naming rules
- PublicApiAnalyzers on Contracts only, since that assembly is the client's real contract

API:
- weather-forecast template removed
- UseHttpsRedirection removed; TLS terminates at the reverse proxy and redirecting
  behind one causes loops
- /healthz/{live,ready,startup}. Liveness deliberately checks no dependencies so a
  transient database outage cannot restart the container and kill live SSH sessions.

Notes:
- No coverage collector yet. Microsoft.Testing.Extensions.CodeCoverage pulls an MTP 1.x
  MSBuild extension that throws TypeLoadException against the MTP 2.3.x xunit.v3 brings.
  Coverage gates are an M3 concern; revisit with an MTP 2.x-aligned version then.

Verified: dotnet build (0 warnings), 17 tests pass, format check clean, API serves
health and OpenAPI endpoints.

src/DodoSSH.Api/DodoSSH.Api.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <!--
+    TargetFramework, Nullable, ImplicitUsings, analyzers and central package
+    management all come from ../../Directory.Build.props.
+  -->
+
+  <ItemGroup>
+    <!-- Integration tests reach Program through WebApplicationFactory<Program>. -->
+    <InternalsVisibleTo Include="DodoSSH.Api.Tests" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" />
+  </ItemGroup>
+
+</Project>

src/DodoSSH.Api/Program.cs

@@ -0,0 +1,26 @@
+using DodoSSH.Api.Setup;
+
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddDodoOpenApi();
+builder.Services.AddDodoHealthChecks();
+
+// DateTime.UtcNow is banned repo-wide (see BannedSymbols.txt); everything takes
+// TimeProvider so time can be faked in tests.
+builder.Services.AddSingleton(TimeProvider.System);
+
+var app = builder.Build();
+
+// Deliberately no UseHttpsRedirection: the API is always fronted by a reverse proxy
+// (Caddy in the reference compose stack) which terminates TLS. Redirecting here
+// produces redirect loops behind a proxy. HTTPS in development comes from the
+// launch profile instead.
+
+app.MapDodoHealthChecks();
+
+if (app.Environment.IsDevelopment())
+{
+    app.MapOpenApi();
+}
+
+await app.RunAsync().ConfigureAwait(false);

src/DodoSSH.Api/Properties/launchSettings.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "http": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": false,
+      "applicationUrl": "http://localhost:5233",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": false,
+      "applicationUrl": "https://localhost:7217;http://localhost:5233",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

src/DodoSSH.Api/Setup/HealthChecks.cs

@@ -0,0 +1,57 @@
+using Microsoft.AspNetCore.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+namespace DodoSSH.Api.Setup;
+
+/// <summary>
+/// Health check wiring.
+/// </summary>
+/// <remarks>
+/// The split between liveness and readiness is deliberate and load-bearing for the
+/// relay: <c>/healthz/live</c> checks the process and nothing else, so a transient
+/// PostgreSQL outage cannot cause the orchestrator to restart the container and
+/// guillotine every live SSH session. Dependency checks belong in
+/// <c>/healthz/ready</c>, which only removes the instance from load balancing.
+/// </remarks>
+internal static class HealthChecks
+{
+    /// <summary>Tag for checks that gate readiness (dependencies).</summary>
+    internal const string ReadyTag = "ready";
+
+    /// <summary>Tag for checks that gate startup completion.</summary>
+    internal const string StartupTag = "startup";
+
+    internal static IServiceCollection AddDodoHealthChecks(this IServiceCollection services)
+    {
+        services.AddHealthChecks();
+
+        // Dependency checks are registered by the milestone that introduces the
+        // dependency, each tagged ReadyTag:
+        //   M1 — PostgreSQL, OIDC discovery + JWKS reachability, pending migrations
+        //   M4 — Data Protection key ring readability
+        return services;
+    }
+
+    internal static WebApplication MapDodoHealthChecks(this WebApplication app)
+    {
+        // Liveness: process is running and the pipeline responds. No dependencies.
+        app.MapHealthChecks("/healthz/live", new HealthCheckOptions
+        {
+            Predicate = _ => false,
+        }).AllowAnonymous();
+
+        // Readiness: safe to route traffic here.
+        app.MapHealthChecks("/healthz/ready", new HealthCheckOptions
+        {
+            Predicate = registration => registration.Tags.Contains(ReadyTag),
+        }).AllowAnonymous();
+
+        // Startup: one-time initialisation finished (K8s startupProbe).
+        app.MapHealthChecks("/healthz/startup", new HealthCheckOptions
+        {
+            Predicate = registration => registration.Tags.Contains(StartupTag),
+        }).AllowAnonymous();
+
+        return app;
+    }
+}

src/DodoSSH.Api/Setup/OpenApi.cs

@@ -0,0 +1,27 @@
+namespace DodoSSH.Api.Setup;
+
+/// <summary>
+/// OpenAPI document configuration.
+/// </summary>
+/// <remarks>
+/// The generated document exists for third parties and a future CLI. It is emitted at
+/// build time to <c>artifacts/openapi/v1.json</c> and diffed in CI so an unintended
+/// contract change fails the pull request. The desktop client's actual contract is the
+/// <c>DodoSSH.Contracts</c> assembly, guarded by PublicApiAnalyzers.
+/// </remarks>
+internal static class OpenApi
+{
+    internal const string DocumentName = "v1";
+
+    internal static IServiceCollection AddDodoOpenApi(this IServiceCollection services)
+    {
+        services.AddOpenApi(DocumentName);
+
+        // Added in M1, once there are endpoints to describe:
+        //   - a document transformer contributing the OAuth2 authorizationCode + PKCE
+        //     security scheme, so the document is usable from a generated client
+        //   - a schema transformer mapping byte[] to {type: string, format: byte},
+        //     since every ciphertext field crosses the wire as base64
+        return services;
+    }
+}

src/DodoSSH.Api/appsettings.Development.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

src/DodoSSH.Api/appsettings.json

@@ -0,0 +1,9 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}

src/DodoSSH.Api/packages.lock.json

@@ -0,0 +1,34 @@
+{
+  "version": 2,
+  "dependencies": {
+    "net10.0": {
+      "Meziantou.Analyzer": {
+        "type": "Direct",
+        "requested": "[3.0.134, )",
+        "resolved": "3.0.134",
+        "contentHash": "tTYCcYKyOko3TMNxmxmA9nakbcHVUgglENmCMIhzIjl9y9FBZO/0tWSxTGC74Sp198FmWih5S5KkjQRBg5ePkQ=="
+      },
+      "Microsoft.AspNetCore.OpenApi": {
+        "type": "Direct",
+        "requested": "[10.0.10, )",
+        "resolved": "10.0.10",
+        "contentHash": "d4Atx9IHq7JgX0F/h7Db+m9zAUzC+cKdI9k+OWnnyQIOUQtfvjIEuhvbjPigVMkAmPUgCbJ8Yp6M9ghUqHtJSQ==",
+        "dependencies": {
+          "Microsoft.OpenApi": "2.0.0"
+        }
+      },
+      "Microsoft.CodeAnalysis.BannedApiAnalyzers": {
+        "type": "Direct",
+        "requested": "[5.6.0, )",
+        "resolved": "5.6.0",
+        "contentHash": "Kcobt3pnOdO0A+6CKiMHZdTEluJpsfxiV20axtZdmfBQnDmiWTKPJADlgAfdTuKNAnVarrkJa0UEGwuOo91muw=="
+      },
+      "Microsoft.OpenApi": {
+        "type": "CentralTransitive",
+        "requested": "[2.11.0, )",
+        "resolved": "2.11.0",
+        "contentHash": "/ignjfdeKT2SGLIR7QEv19KnI0rvoxRG/TYDOZdK9EsWLjKK9IK8i1Mo5NRm9PRV3i64DzlTqnIflWvoyfljLg=="
+      }
+    }
+  }
+}