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.

src/DodoSSH.Client.Android/Properties/AndroidManifest.xml

@@ -18,6 +18,25 @@
   <!-- Releases the device key. See AndroidDeviceKeyStore. -->
   <uses-permission android:name="android.permission.USE_BIOMETRIC" />
 
+  <!--
+    ◆ Hands a downloaded APK to the system installer, which is the whole of this head's updater. See
+    AndroidUpdateChannel and ADR 0014.
+
+    It is worth being exact about what this permission is and is not. It does not let this application
+    install anything: it lets it *ask*, and the platform then shows its own confirmation naming the
+    package and the source. On API 26 and later it is additionally gated by a per-application setting the
+    user has to turn on in Settings, which no permission dialogue can grant — so the first update walks
+    them there. Nothing is installed without two deliberate answers, neither of them to a screen this
+    application drew.
+
+    Declared rather than avoided by opening the release page in a browser. That would work, and it would
+    move the same install through Chrome's downloads and the same unknown-sources gate with one more step
+    and no less trust. What it would also do is give up any way of knowing a fix has been fetched, which
+    for an SSH client holding a team's credentials is the property ADR 0011's consequences call the
+    sharpest edge of shipping outside a store.
+  -->
+  <uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES" />
+
   <!--
     allowBackup and fullBackupContent are both off deliberately, and both are vault properties rather
     than defaults worth inheriting. The local cache is a SQLite file holding the ciphertext mirror, the
@@ -32,7 +51,13 @@
     that attribute exists so a launcher wanting a circle can be handed a second bitmap, and
     an adaptive icon is already masked to whatever shape the launcher asks for.
   -->
-  <application android:label="DodoSSH"
+  <!--
+    @string/app_name rather than the literal that was here, because the two channels are two installable
+    applications and both showing "DodoSSH" under the launcher icon is a home screen nobody can read. The
+    release channel's copy of that string is exactly what was written here before. See
+    Resources/values/strings.xml, and MainActivity, which has to name the same resource.
+  -->
+  <application android:label="@string/app_name"
                android:icon="@mipmap/ic_launcher"
                android:theme="@style/DodoTheme"
                android:networkSecurityConfig="@xml/network_security_config"