feat: Gemini AI (doc OCR + face match) + role-assignment endpoints

- GeminiService (integrations/gemini, @Global): extractDocument (OCR fields) + faceMatch; graceful if no GEMINI_API_KEY
- documents: face-match now real via Gemini; POST /admin/documents/:id/ocr extracts fields for CS auto-fill
- roles: PATCH /admin/users/:id/role (admin) + POST /platform/users/role (bootstrap via x-platform-secret)
- config: gemini + platform.secret; .env.example entries

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/driver/trip_overlay_plugin/README.md

@@ -0,0 +1,15 @@
+# trip_overlay_plugin
+
+A new Flutter plugin project.
+
+## Getting Started
+
+This project is a starting point for a Flutter
+[plug-in package](https://flutter.dev/to/develop-plugins),
+a specialized package that includes platform-specific implementation code for
+Android and/or iOS.
+
+For help getting started with Flutter development, view the
+[online documentation](https://docs.flutter.dev), which offers tutorials,
+samples, guidance on mobile development, and a full API reference.
+