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/

compliance_test.go

@@ -0,0 +1,8 @@
+package firebase_test
+
+import (
+	"code.nochebuena.dev/go/firebase"
+	"code.nochebuena.dev/go/logz"
+)
+
+var _ firebase.Component = firebase.New(logz.New(logz.Options{}), firebase.Config{ProjectID: "test"})