feat(kevin_bridge): exit-scan daily job + cursor + audit writer

services/kevin_signal_bridge/cursor.py

@@ -0,0 +1,28 @@
+"""Redis-backed cursor for the bridge.
+
+Tracks the highest `kevin_stock_mentions.id` we've already attempted to
+process. Stored at key `kevin:bridge:last_mention_id`.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+
+class RedisCursor:
+    _KEY = "kevin:bridge:last_mention_id"
+
+    def __init__(self, redis: Any) -> None:
+        self.redis = redis
+
+    async def last_seen_id(self) -> int:
+        v = await self.redis.get(self._KEY)
+        if v is None:
+            return 0
+        return int(v)
+
+    async def advance(self, mention_id: int) -> None:
+        # Conservative: only set if mention_id > current
+        current = await self.last_seen_id()
+        if mention_id > current:
+            await self.redis.set(self._KEY, str(mention_id))