Update: 将子项目从 submodule 转为完整内容

- 移除 GovAI, nomifun-tauri, 算力盒子 的 submodule 引用
- 添加所有子项目的完整源代码
- 保留原始 .git 为 .git.bak 备份

nomifun-tauri/crates/backend/nomifun-db/migrations/022_messages_keyset_index.sql

@@ -0,0 +1,22 @@
+-- Keyset (cursor) pagination for conversation message history.
+--
+-- An ever-growing single conversation — notably a desktop companion's ONE
+-- session, which now also absorbs every IM-channel turn — is loaded in
+-- newest-first windows via a (created_at, id) keyset cursor instead of one
+-- giant fetch:
+--
+--   SELECT * FROM messages
+--   WHERE conversation_id = ?
+--     AND type NOT IN ('cron_trigger','skill_suggest')
+--     AND (created_at < ? OR (created_at = ? AND id < ?))
+--   ORDER BY created_at DESC, id DESC
+--   LIMIT ?
+--
+-- The existing idx_messages_conv_created / idx_messages_conv_created_desc cover
+-- (conversation_id, created_at) but NOT the `id` tiebreaker, so the cursor's
+-- (created_at, id) comparison and the matching ORDER BY degrade to a sort. This
+-- composite covers both, keeping deep "load older" pages index-only and stable
+-- under concurrent streaming appends. `id` is msg_{uuidv7} (time-ordered), so it
+-- is a sound, monotonic tiebreaker for rows sharing a created_at millisecond.
+CREATE INDEX IF NOT EXISTS idx_messages_conv_created_id
+    ON messages (conversation_id, created_at DESC, id DESC);