feat: fold bot-bottle-orchestrator into bot_bottle/orchestrator subpackage

Moves the orchestrator into bot_bottle/orchestrator/ so one install gets
everything. Entry point is now `python -m bot_bottle.orchestrator run`.

- Add bot_bottle/orchestrator/ with all 14 modules (verbatim move; internal
  imports were already relative, so no changes inside orchestrator modules)
- Rewrite bootstrap.py: remove the lazy bot_bottle import guard, use direct
  relative imports from ..contrib.*
- Add bot_bottle/contrib/forge/base.py: ScopedForge (read-anywhere / write-scoped)
- Add bot_bottle/contrib/gitea/client.py: GiteaClient + GiteaForge (urllib.request only)
- Add bot_bottle/contrib/gitea/forge_state.py: ForgeState + SqliteForgeStateStore
- Add tests/unit/orchestrator/ (82 tests: 63 migrated + 19 new for contrib modules)

Closes #321

bot_bottle/orchestrator/watchdog.py

@@ -0,0 +1,68 @@
+"""Watchdog: freeze runs whose agent exited without signalling done.
+
+`sweep(now)` is the pure, testable core: any `running` record whose
+`last_checkin_at` is older than the timeout is frozen as
+done-without-self-report and returned so provenance can flag it.
+`Watchdog.start()` runs `sweep` on a daemon thread once a minute.
+"""
+
+from __future__ import annotations
+
+import threading
+from datetime import datetime, timedelta
+
+from .model import STATUS_FROZEN, STATUS_RUNNING, RunRecord
+from .runner import BottleRunner
+from .store import StateStore
+
+_TICK_SECS = 60.0
+
+
+def _parse(ts: str) -> datetime | None:
+    try:
+        return datetime.fromisoformat(ts)
+    except (ValueError, TypeError):
+        return None
+
+
+class Watchdog:
+    def __init__(
+        self,
+        *,
+        store: StateStore,
+        runner: BottleRunner,
+        timeout_secs: int,
+    ) -> None:
+        self._store = store
+        self._runner = runner
+        self._timeout = timedelta(seconds=timeout_secs)
+        self._stop = threading.Event()
+        self._thread: threading.Thread | None = None
+
+    def sweep(self, now: datetime) -> list[RunRecord]:
+        """Freeze stale running records. Returns the ones fired."""
+        fired: list[RunRecord] = []
+        for record in self._store.all():
+            if record.status != STATUS_RUNNING:
+                continue
+            checkin = _parse(record.last_checkin_at)
+            if checkin is None or now - checkin <= self._timeout:
+                continue
+            self._runner.freeze(record.slug)
+            record.status = STATUS_FROZEN
+            self._store.upsert(record)
+            fired.append(record)
+        return fired
+
+    def start(self) -> None:
+        self._thread = threading.Thread(target=self._loop, daemon=True)
+        self._thread.start()
+
+    def stop(self) -> None:
+        self._stop.set()
+        if self._thread is not None:
+            self._thread.join(timeout=_TICK_SECS)
+
+    def _loop(self) -> None:
+        while not self._stop.wait(_TICK_SECS):
+            self.sweep(datetime.now().astimezone())