feat(plugin-firebase): add Cloud Firestore and Realtime Database driver

[i87ce]

Why

TablePro could not open either Firebase database.

Change

• One registry plugin, Firebase Driver, serving two connection types: Cloud Firestore and Firebase Realtime Database. Service account key, Application Default Credentials or the emulators, with the project taken from the credential.
• Firestore: root collections and discovered subcollections (as */id collection groups) in the sidebar, documents in the grid, filters and sorts as structured queries, cell edits typed by the value they replace, Edit Document guarded by the update time.
• Realtime Database: the project's instances in the database switcher, a node's children as rows, per-node edits guarded by the ETag.
• A denial from IAM or the security rules reads "Permission denied" with the operation, never an empty table.

Verified

Unit tests for the core and the driver, plus emulator suites that run when FIRESTORE_EMULATOR_HOST and FIREBASE_DATABASE_EMULATOR_HOST are set. Read-only checks against live projects with ADC, and the Debug app opening both types against the emulators. No UI test: the flow needs a running emulator.

Not in this PR

• The docs page: docs(databases): add the Firebase page for Firestore and Realtime Database docs#13, a draft until this merges.
• Real-time listeners.

Fixes #2504

🤖 Generated with Claude Code

[i87ce]

Thanks for merging and for the cleanup. Could you cut plugin-firebase-v1.0.0 when you have a moment, so the plugin reaches the registry? The docs page is ready in TableProApp/docs#13.