Let the phone replace itself, and give CI a channel it may sign

The Android head had no updater and no release path, and the two are one problem:
Android refuses an update signed by a different key, and CI generates a fresh debug
key in every container. An APK released from a workflow could be installed once and
never updated again — each new one an uninstall, which on this product means losing
the cache, the outbox and the device key.

So there are two channels, and they are two applications because the platform gives
no third option. dev.dodotech.dodossh is cut from a v* tag by a person running
scripts/release-android.ps1 with the key ADR 0011 rule 1 keeps off runners.
dev.dodotech.dodossh.nightly is cut from main by CI and signed with a keystore
committed here in the open — a key everybody has cannot be stolen and grants nothing
by being held, which is why putting it in CI does not touch the rule. Neither can
update the other, by construction. See ADR 0014.

The android job assumed an image with a JDK and an Android SDK on it, which is what
a GitHub runner is and what this project's is not. It now installs a JDK, fetches
Google's command-line tools, accepts the licences and installs API 36 — each a no-op
where it is already satisfied, and each cached by the persistent runner's own disk
rather than by an action that would move a quarter of a gigabyte to rebuild a
directory that never left.

The client reads a small JSON manifest beside the APK, the counterpart of
releases.win.json, and compares Android's versionCode rather than a version name:
that integer is what the platform itself uses to accept or refuse an install, so
comparing anything else would offer updates the phone then rejects. It fetches, and
then asks Android to ask — the system draws its own confirmation, and from API 26
will not draw even that until unknown sources is on for this application.

IUpdateChannel gained ApplyingEndsTheProcess. On Windows applying replaces the files
and restarts, so the shell disposes the vault first and that is what zeroes the keys.
On the phone the install is a request and the answer may be no, so disposing first
would answer "not now" with a locked keychain and every shell closed — a punishment
for declining an update.

Two measured bugs found on the way, both older than this work and both invisible to
a -getProperty check. ApplicationDisplayVersion is read by the Android targets in a
top-level PropertyGroup, so the target setting it from MinVer ran after the only
thing that reads it: every APK ever built here said versionName 1.0.0. And nothing
found so far varies the launcher name per channel — four mechanisms tried, all of
them recorded in platform-flags, none of them reaching the label the launcher shows.
The two channels share an icon name for now and are told apart by package name,
version, and what the preferences screen says.

docs/platform-flags.md

@@ -616,3 +616,29 @@ surface — but it is still an unmetered write path.
 **`/api/v1/me` does not update `last_seen_at_utc`.** Deliberate: a GET that writes on every call is
 a smell, and nothing depends on the value yet. Revisit when device management lands, since that is
 the first feature that needs it.
+
+**`ApplicationDisplayVersion` cannot be set from a target, so the Android head shipped `1.0.0`.**
+`Xamarin.Android.Common.targets` reads it in a plain top-level `PropertyGroup` —
+`<_AndroidVersionName>$(ApplicationDisplayVersion)</_AndroidVersionName>` — which is *evaluation*, not a
+target. Every project property is already final before any target runs, so the MinVer-derived value set in
+`UseTheDerivedVersionForAndroid` was assigned after the only thing that reads it had finished. MinVer cannot
+run at evaluation time, so no arrangement of the public property works. The tell is that
+`-getProperty:ApplicationDisplayVersion` answers correctly while `aapt2 dump badging` on the packaged APK
+says `versionName='1.0.0'` — measured, and the reason a `-getProperty` check cannot catch this class of bug.
+The fix is to assign `_AndroidVersionName` from a target hooked `BeforeTargets="_GenerateJavaStubs"`; an
+internal name, taken deliberately over passing `-p:ApplicationDisplayVersion` from every caller and leaving
+an ordinary `dotnet build` lying about its version.
+
+**Nothing found so far varies the Android launcher name per build.** Four mechanisms were tried and all
+four produce the same label. `AndroidManifestPlaceholders` is wired to the manifest task and does not reach
+`android:label` — measured on a build whose placeholder property evaluated to `appLabel=DodoSSH nightly`
+and whose APK reported `DodoSSH`. `ApplicationTitle`, the documented property, feeds an `ApplicationLabel`
+task parameter that the label already on the application element wins against. A second resource directory
+under `Resources/` is picked up by the SDK's own glob as a *qualifier* and fails the build outright with
+`APT2142: invalid configuration 'nightly'`. And an `AndroidResource` `Remove`/`Include` swap does nothing
+from the project body — the SDK's glob is added by `Sdk.targets`, imported below it, so the removal runs
+before the item exists — while the same swap inside a target that runs before `UpdateAndroidResources` also
+had no effect. Underneath all of it: the launcher shows the *activity's* label, and that one is a string in
+a C# attribute. The two channels ADR 0014 defines therefore share a launcher name, and are told apart by
+the package name in Android's app info, by the version, and by the channel the application names on its own
+preferences screen.