feat: Phase 6 — require_active_service decorator + wizard install wiring

Email/calendar/files routes now return 404 when the service is not
installed, using a require_active_service decorator that checks
ServiceRegistry. Status endpoints are exempt so health checks always work.

SetupManager.complete_setup() now accepts a service_store_manager and
installs any wizard-selected services in a background daemon thread after
setup completes. Failures are logged but do not fail the wizard.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/routes/__init__.py

@@ -0,0 +1,19 @@
+from functools import wraps
+from flask import jsonify
+
+
+def require_active_service(service_id: str):
+    """Decorator: return 404 if the named service is not installed.
+
+    Apply to all email/calendar/files routes except /status endpoints,
+    so the UI can always check installation state without being blocked.
+    """
+    def decorator(fn):
+        @wraps(fn)
+        def wrapper(*args, **kwargs):
+            from app import service_registry
+            if service_registry.get(service_id) is None:
+                return jsonify({'error': f'Service {service_id!r} is not installed'}), 404
+            return fn(*args, **kwargs)
+        return wrapper
+    return decorator