feat(firebase): initial stable release v0.9.0

Firebase App component with launcher lifecycle and health check integration.

What's included:
- Config with ProjectID (FIREBASE_PROJECT_ID env var); credentials via ADC
- Provider interface exposing native *firebase.App directly
- Component interface: launcher.Component + health.Checkable + Provider
- New(logger, cfg) constructor for lifecycle registration via lc.Append
- Health check via GetUser("health-probe-non-existent") + auth.IsUserNotFound at LevelCritical
- No-op OnStop (Firebase Admin SDK has no Close method)

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

.gitignore

@@ -0,0 +1,38 @@
+# Binaries
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with go test -c
+*.test
+
+# Output of go build
+*.out
+
+# Dependency directory
+vendor/
+
+# Go workspace file
+go.work
+go.work.sum
+
+# Environment files
+.env
+.env.*
+
+# Editor / IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# VCS files
+COMMIT.md
+RELEASE.md