feat: utterances API routes — list, clip, tag, dismiss

Adds app/api/main.py (create_app factory with health endpoint), utterances
router (GET /api/utterances with date/room/speaker/status filters, GET clip,
POST tag, POST dismiss), stub routers for speakers/rooms/search/rag, and
tests/routes/ with 6 passing TDD tests.

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

app/api/routes/rag.py

@@ -0,0 +1,6 @@
+from fastapi import APIRouter
+
+
+def make_router(settings, db_factory):
+    router = APIRouter(prefix="/api")
+    return router