What does this PR do?

`_listen_loop()` in `gateway/platforms/qqbot/adapter.py` has three paths where `MAX_RECONNECT_ATTEMPTS` is reached and the loop exits via `return` — but none of them call `_set_fatal_error()` or `_notify_fatal_error()`. The gateway runner keeps the platform state as the last `_mark_connected()` value (connected), while the adapter is silently dead. Because the gateway process itself does not exit, `systemd Restart=on-failure` never fires.

Three exhaustion paths are affected:

• 4008 rate-limit branch — bare `return` with no `logger.error`, no `_set_fatal_error()`, no `_notify_fatal_error()`
• QQCloseError general branch — has `logger.error` but no `_set_fatal_error()` or `_notify_fatal_error()`
• Exception branch — has `logger.error` but no `_set_fatal_error()` or `_notify_fatal_error()`

Fix: add `_set_fatal_error("qq_reconnect_exhausted", ..., retryable=False)` followed by `await self._notify_fatal_error()` to all three paths. `_set_fatal_error()` alone only writes to the status file — `_notify_fatal_error()` is required to invoke the GatewayRunner's `_handle_adapter_fatal_error` handler, which disconnects the adapter and triggers `systemd Restart=on-failure`. This matches the pattern already used in the Telegram adapter (`gateway/platforms/telegram.py` lines 366, 460).

Related Issue

Fixes #14539

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor
• 🎯 New skill

Changes Made

• `gateway/platforms/qqbot/adapter.py`: add `_set_fatal_error()` + `await _notify_fatal_error()` before each of the three `return` points in `_listen_loop()` (+18 lines)
• `tests/gateway/test_qqbot.py`: add `TestListenLoopReconnectExhaustion` with one test per exhaustion path, each asserting both `has_fatal_error` and `_notify_fatal_error` was awaited (+100 lines)

How to Test

Requires a live QQ Bot setup. Unit tests cover all three paths:

```bash
pytest tests/gateway/test_qqbot.py::TestListenLoopReconnectExhaustion -v
```

All 3 tests pass.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix
• I've run `pytest tests/gateway/test_qqbot.py -v` and pre-existing failures are unrelated to this change (they require `pytest-asyncio` which is in dev deps)
• I've added tests for my changes
• I've tested on my platform: macOS

Documentation & Housekeeping

• I've updated relevant documentation — or N/A
• I've updated `cli-config.yaml.example` — or N/A
• I've updated `CONTRIBUTING.md` or `AGENTS.md` — or N/A
• I've considered cross-platform impact — or N/A
• I've updated tool descriptions/schemas — or N/A