feat(bootstrap,api,infra): scaffold app composition, health route, and postgres/minio/qdrant adapters

Why:
- first runnable slice of ADR-0012's resource-lifetime rules and ADR-0015's package layout: app-lifetime clients built once in the lifespan, released via explicit dependencies.

Changes:
- Settings split into per-domain nested settings (postgres/minio/ingestion/qdrant/app/logging); FastAPI app wired with /healthz, /readyz and a /v1 router; Postgres/MinIO/Qdrant adapters and SQLAlchemy models for tenants, API keys, source files, ingestion jobs/events.

src/api/router.py

@@ -0,0 +1,3 @@
+from fastapi import APIRouter
+
+router = APIRouter()

src/api/routers/health.py

@@ -0,0 +1,36 @@
+import asyncio
+
+from fastapi import APIRouter, Request, Response, status
+
+from src.bootstrap.dependencies import AppResources
+from src.infrastructure.minio.client import ping as ping_minio
+from src.infrastructure.postgres.database import ping as ping_postgres
+from src.infrastructure.qdrant.client import ping as ping_qdrant
+
+router = APIRouter(tags=["health"])
+
+
+@router.get("/healthz")
+async def healthz() -> dict[str, str]:
+    return {"status": "ok"}
+
+
+@router.get("/readyz")
+async def readyz(request: Request, response: Response) -> dict[str, bool]:
+    resources: AppResources = request.app.state.resources
+    timeout = resources.settings.app.readiness_check_timeout_seconds
+
+    postgres_ready, minio_ready, qdrant_ready = await asyncio.gather(
+        ping_postgres(resources.db_engine, timeout),
+        ping_minio(resources.minio_client, timeout),
+        ping_qdrant(resources.qdrant_client, timeout),
+    )
+
+    result = {
+        "postgres": postgres_ready,
+        "minio": minio_ready,
+        "qdrant": qdrant_ready,
+    }
+    if not all(result.values()):
+        response.status_code = status.HTTP_503_SERVICE_UNAVAILABLE
+    return result