feat: on-the-fly SMS translation via offline-translator AIDL

Adds a small `:translate` Gradle module that translates received SMS /
MMS bubbles and conversation-list snippets on the fly by binding to the
offline-translator app on F-Droid (`dev.davidv.translator`). The actual
translation runs there — Mozilla Bergamot/Marian on-device — so this
patch ships no model, no inference, and no permissions beyond an
Android 11+ <queries> block for package visibility.

Behavior:
- User-defined source-language allowlist + target language in
  Settings → Translation (right after Language). Off by default.
- Auto-translate fires on RecyclerView bind for received bubbles and
  conversation snippets. Detection uses ML Kit Language Identification
  (CLD3, on-device). Once dev.davidv.translator exposes a
  detectLanguage() AIDL method we'll route through that and drop ML Kit.
- AIDL latency is sub-second, so the bubble just quietly swaps from
  the original to the translation — no loading spinner.
- Tap the translate icon next to a bubble to flip it back to the
  original; tap again to flip to the translation. Cached in process
  memory.
- Long-press → ⋮ → Translate forces a one-off translation regardless
  of the allowlist (useful for messages in non-allowlisted languages),
  with a toast surfacing AIDL errors like 'language pack not installed'.
- Copy / Share / Select on a translated bubble captures what the user
  sees, not the underlying source body.
- Silently no-ops when offline-translator isn't installed; settings
  screen shows an F-Droid install banner.
- Translation Settings is a regular Fossify sub-screen with
  MyAppBarLayout + MaterialToolbar + NestedScrollView, matching
  Manage Blocked Numbers / Keywords / SettingsActivity.

No new database, no service, no boot receiver, no foreground service.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

translate/src/main/aidl/dev/davidv/translator/ITranslationService.aidl

@@ -0,0 +1,7 @@
+package dev.davidv.translator;
+
+import dev.davidv.translator.ITranslationCallback;
+
+interface ITranslationService {
+    void translate(String textToTranslate, String fromLanguage, String toLanguage, ITranslationCallback callback);
+}