Wire up FCM push notification service

- ClippyFCMService: Receives FCM data messages, routes to TTS pipeline
- FCMTokenManager: Stores FCM token in Matrix account data for n8n
- Enable Google Services plugin and Firebase dependencies
- Add FCM service to AndroidManifest.xml
- Register FCM token on app init in ClippySession and SetupActivity

Token stored at: /_matrix/client/v3/user/@clippyauto:hobbs.farm/account_data/farm.hobbs.clippy.fcm_token

Co-authored-by: Spirit <spirit@hobbs.farm>

build.gradle.kts

@@ -2,6 +2,5 @@ plugins {
     id("com.android.application") version "8.7.3" apply false
     id("org.jetbrains.kotlin.android") version "2.1.10" apply false
     id("org.jetbrains.kotlin.plugin.serialization") version "2.1.10" apply false
-    // Firebase deferred to Sprint 2 (needs google-services.json)
-    // id("com.google.gms.google-services") version "4.4.2" apply false
+    id("com.google.gms.google-services") version "4.4.2" apply false
 }