feat: add backend document database

.memory/worklog.json

@@ -1,11 +1,5 @@
 {
   "entries": [
-    {
-      "files_changed": 3,
-      "message": "Codex 会话活跃 · 最近命令：codex · 3 项未提交变更 · 最近提交：auto-save 2026-05-15 17:50 (~1)",
-      "ts": "2026-05-15T09:54:48Z",
-      "type": "session-heartbeat"
-    },
     {
       "files_changed": 4,
       "hash": "a662130",
@@ -3257,6 +3251,13 @@
       "message": "auto-save 2026-05-18 15:13 (~8)",
       "hash": "2a1aa4c",
       "files_changed": 8
+    },
+    {
+      "ts": "2026-05-18T15:29:47+08:00",
+      "type": "commit",
+      "message": "auto-save 2026-05-18 15:29 (+1, ~5)",
+      "hash": "1c451c6",
+      "files_changed": 6
     }
   ]
 }