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>

tests/routes/conftest.py

@@ -0,0 +1,18 @@
+import pytest
+from fastapi.testclient import TestClient
+
+
+@pytest.fixture
+def api_client(settings):
+    from app.api.main import create_app
+    app = create_app(settings)
+    return TestClient(app)
+
+
+@pytest.fixture
+def seeded_db(db):
+    """DB with a room and speaker pre-inserted."""
+    db.execute("INSERT INTO rooms (name) VALUES (?)", ("Kitchen",))
+    db.execute("INSERT INTO speakers (name) VALUES (?)", ("Jeremy",))
+    db.commit()
+    return db