feat(android): boot-time autostart, capture watchdog, versionCode from git

Boot-time startup so LedGrab has display capture and control without user
interaction on rooted TV boxes. Also folds in a batch of review findings
from the Android package audit.

Autostart
- BootReceiver fires on BOOT_COMPLETED / LOCKED_BOOT_COMPLETED /
  MY_PACKAGE_REPLACED, gated by AutostartPrefs and Root.looksRooted().
  Dispatches CaptureService.createRootIntent via
  ContextCompat.startForegroundService. Unrooted devices are a no-op
  because MediaProjection consent cannot be bypassed silently.
- AutostartPrefs: thin SharedPreferences wrapper, defaults to enabled.
  Exposed as a CheckBox on the stopped panel; greyed out when not rooted.
- Manifest: RECEIVE_BOOT_COMPLETED, REQUEST_IGNORE_BATTERY_OPTIMIZATIONS,
  WAKE_LOCK permissions + the new BootReceiver.
- MainActivity prompts for battery-optimization exemption on first opt-in
  so Doze/App Standby doesn't kill the FG service on phones.

Service stability
- onStartCommand now flips isRunning only after startForeground succeeds
  (was stuck=true forever if the FG transition threw) and resets on
  exception. Returns START_REDELIVER_INTENT for root mode so the OS can
  restart the service with the original intent (no consent token to
  invalidate); MediaProjection mode keeps START_NOT_STICKY.
- Watchdog coroutine monitors RootScreenrecord.framesDelivered. Respawns
  the pipeline on stall (reusing the existing Python bridge — no server
  restart), caps at 3 consecutive restarts before giving up.
- RootScreenrecord.framesDelivered is now an AtomicInteger, exposed as a
  public property for the watchdog.
- ScreenCapture takes an onProjectionStopped lambda; when the user taps
  the system Cast/Screen-capture stop banner, the whole service is torn
  down instead of leaving a stale FG notification.
- MainActivity's two startForegroundService calls switch to
  ContextCompat.startForegroundService, clearing pre-existing NewApi lint
  errors (minSdk=24 < API 26 native method).

Build
- versionCode derived from git rev-list --count HEAD (or the
  ANDROID_VERSION_CODE env var for CI). Was pinned to 1 — sideload
  upgrades were silently refusing to install.
- New i18n strings (autostart_label, autostart_unavailable, version_prefix)
  in en/ru/zh; version_text now uses the resource instead of string
  concat.

TODO.md: new "Android Autostart on Boot" section tracking done/pending
items; real-hardware verification on a Magisk'd TV box is the remaining
checkbox.

android/app/src/main/res/layout/activity_main.xml

@@ -52,6 +52,18 @@
             android:textSize="22sp"
             android:focusable="true"
             android:focusableInTouchMode="true" />
+
+        <CheckBox
+            android:id="@+id/autostart_check"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="32dp"
+            android:text="@string/autostart_label"
+            android:textColor="@color/text_secondary"
+            android:textSize="20sp"
+            android:buttonTint="@color/teal_accent"
+            android:focusable="true"
+            android:focusableInTouchMode="true" />
     </LinearLayout>
 
     <!-- Version at bottom -->