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/macos/Runner/MainFlutterWindow.swift

@@ -0,0 +1,15 @@
+import Cocoa
+import FlutterMacOS
+
+class MainFlutterWindow: NSWindow {
+  override func awakeFromNib() {
+    let flutterViewController = FlutterViewController()
+    let windowFrame = self.frame
+    self.contentViewController = flutterViewController
+    self.setFrame(windowFrame, display: true)
+
+    RegisterGeneratedPlugins(registry: flutterViewController)
+
+    super.awakeFromNib()
+  }
+}