script-mode task execution — database-backed tasks with direct script runner

Tasks now live in the database (mode: script or agentic). Script-mode tasks
bypass the agent entirely — the implementation is materialized to a temp file
and executed directly, with stdout/stderr streamed to the UI via WebSocket.

Includes convert-to-mp3 as the first native script task.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/databases/officer_db/migrations/meta/_journal.json

@@ -15,6 +15,13 @@
       "when": 1772799835768,
       "tag": "0001_freezing_carmella_unuscione",
       "breakpoints": true
+    },
+    {
+      "idx": 2,
+      "version": "7",
+      "when": 1772985087180,
+      "tag": "0002_cute_doorman",
+      "breakpoints": true
     }
   ]
 }