feat(search): add role-aware backend search and truthful n8n status

Two new endpoints. GET /api/v1/search returns bounded typed results
(vehicle, booking, data-quality-issue, application section) instead of the
frontend guessing routes from regex patterns against public-ref prefixes;
data-quality and manager-only sections are filtered server-side by role,
and customers are deliberately never returned since no customer detail
route exists in this PoC.

GET /api/v1/integrations/status aggregates outbox delivery counts
(pending/delivering/succeeded/failed) into a single truthful n8n state
(disabled/unavailable/degraded/operational/no_evidence) instead of the UI
showing whichever status the single most recent event happened to be in --
a vehicle_status_conflict-style bug where one stale failure or one lucky
success could misreport the dispatcher's actual health.

Also fixes a real config gap this surfaced: MCP_HUB_REGISTRATION_ENABLED
was documented in .env.example but had no corresponding Settings field, so
it was silently ignored by pydantic-settings' extra="ignore" and never
actually read anywhere in the codebase.

backend/app/main.py

@@ -11,9 +11,11 @@ from app.api.routers import (
     dashboard,
     data_quality,
     demo,
+    integration_status,
     integrations,
     knowledge,
     mcp_integrations,
+    search,
     vehicles,
     workflows,
 )
@@ -88,3 +90,5 @@ app.include_router(workflows.router)
 app.include_router(integrations.router)
 app.include_router(knowledge.router)
 app.include_router(mcp_integrations.router)
+app.include_router(search.router)
+app.include_router(integration_status.router)