feat: add sessions endpoints with close mechanism

src/backend/api/routes/sessions.py

@@ -0,0 +1,37 @@
+from fastapi import APIRouter, Depends
+from starlette.responses import JSONResponse
+
+from src.backend.api.dependencies import verify_api_key
+from src.backend.db.database import get_db, list_sessions, close_session
+from src.backend.models.api import ok, fail
+
+router = APIRouter(
+    prefix="/sessions",
+    tags=["sessions"],
+    dependencies=[Depends(verify_api_key)],
+)
+
+
+async def _get_db():
+    db = await get_db()
+    try:
+        yield db
+    finally:
+        await db.close()
+
+
+@router.get("", summary="List sessions")
+async def list_all(db=Depends(_get_db)):
+    sessions = await list_sessions(db)
+    return ok(sessions)
+
+
+@router.delete("/{session_id}", summary="Close session")
+async def delete(session_id: str, db=Depends(_get_db)):
+    closed = await close_session(db, session_id)
+    if not closed:
+        return JSONResponse(
+            status_code=404,
+            content=fail("NOT_FOUND", "Session not found"),
+        )
+    return ok({"closed": True})