feat: openclaw-style secrets (env.vars + \) and per-task model routing

- Replace python-dotenv with config.json env.vars block + \ substitution
- Add models section for per-task model routing (heartbeat, subagent, default)
- Heartbeat/subagent tasks can use different models/providers than main chat
- Remove python-dotenv from dependencies
- Update all docs to reflect new config approach
- Reorganize docs into project/ and research/ subdirectories

scheduler/store.py

@@ -147,6 +147,22 @@ class JobStore:
             conn.commit()
             return cursor.rowcount
 
+    def remove_by_channel_type(self, channel_type: str) -> list[str]:
+        """Remove all jobs with the given channel_type. Returns removed IDs."""
+        with self._conn() as conn:
+            rows = conn.execute(
+                "SELECT id FROM jobs WHERE channel_type = ?", (channel_type,)
+            ).fetchall()
+            ids = [row["id"] for row in rows]
+            if ids:
+                conn.execute(
+                    "DELETE FROM jobs WHERE channel_type = ?", (channel_type,)
+                )
+                conn.commit()
+        if ids:
+            logger.info(f"Removed {len(ids)} jobs with channel_type={channel_type}")
+        return ids
+
     @staticmethod
     def _row_to_job(row: sqlite3.Row) -> ScheduledJob:
         return ScheduledJob(