feat(history): 消息搜索/编辑/删除 + 会话置顶(D2/D3/D5)

- history/message_ops.go(新): Search(会话内, q/after互斥, LIKE参数化+%/_转义+大小写不敏感, 严格限定会话doc) / UpdateMessage(返回更新后Message) / DeleteMessage / messageByID / escapeLike
- history/session_pin.go(新): SetPinned; 迁移0009 chat_sessions加pinned INTEGER DEFAULT 0; store.go SessionMeta.Pinned + createSessionsTable加列
- session_preview.go: 查询加s.pinned + ORDER BY pinned DESC,(type=main) DESC,created_at ASC
- gateway history_write.go(新,保持history.go≤500): handlePatchSession(pinned+title) / handlePatchMessage / handleDeleteMessage; server.go加PATCH/DELETE /api/v1/messages/{id} + /sessions/{id}置顶
- history.go: handleListMessages读q分流Search; 契约PATCH title/置顶
- D2会话内搜索(不做跨会话,隔离会话不外泄红线); D3不做重发端点(客户端编辑后再发); D5用pinned bool
- 测试(message_ops/history_messages/migrate_pinned), build/vet/test绿+3平台交叉编译; Docs/api-client v0.30
- 未做: 编辑/删除WS实时广播(message_edited/deleted), 下批

internal/services/gateway/server.go

@@ -124,9 +124,21 @@ type HistoryStore interface {
 	ListAdapterLog(ctx context.Context, adapterID string, before int64, limit int) ([]history.Message, error)
 	ListAllLog(ctx context.Context, before int64, limit int) ([]history.Message, error)
 	DeleteSession(ctx context.Context, sessionID string) error
+	// Search returns session-scoped content matches (newest first) for the
+	// ?q= message-search path. An empty query yields an empty slice.
+	Search(ctx context.Context, sessionID, query string, before int64, limit int) ([]history.Message, error)
+	// UpdateMessage edits a single message's content and returns the updated
+	// message. An unknown id returns history.ErrMessageNotFound.
+	UpdateMessage(ctx context.Context, id, content string) (history.Message, error)
+	// DeleteMessage removes a single message. An unknown id returns
+	// history.ErrMessageNotFound.
+	DeleteMessage(ctx context.Context, id string) error
 	// RenameSession sets a session's display title (main or sub). An unknown id
 	// returns history.ErrSessionNotFound.
 	RenameSession(ctx context.Context, sessionID, title string) error
+	// SetPinned pins/unpins a session (main or sub). An unknown id returns
+	// history.ErrSessionNotFound.
+	SetPinned(ctx context.Context, sessionID string, pinned bool) error
 	NewSubSession(ctx context.Context, ownerID string) (string, error)
 	ListSessions(ctx context.Context) ([]history.SessionMeta, error)
 }
@@ -471,7 +483,11 @@ func (s *Server) Handler() http.Handler {
 	mux.Handle("GET /api/v1/sessions/{id}/messages", historyAuth(http.HandlerFunc(s.handleListMessages)))
 	mux.Handle("POST /api/v1/sessions", historyAuth(http.HandlerFunc(s.handleCreateSubSession)))
 	mux.Handle("DELETE /api/v1/sessions/{id}", historyAuth(http.HandlerFunc(s.handleDeleteSession)))
-	mux.Handle("PATCH /api/v1/sessions/{id}", historyAuth(http.HandlerFunc(s.handleRenameSession)))
+	mux.Handle("PATCH /api/v1/sessions/{id}", historyAuth(http.HandlerFunc(s.handlePatchSession)))
+	// Single-message edit/delete (Android collaboration batch ③a, D3). A message is
+	// addressed by its own opaque id; both are owner/admin-gated history writes.
+	mux.Handle("PATCH /api/v1/messages/{id}", historyAuth(http.HandlerFunc(s.handlePatchMessage)))
+	mux.Handle("DELETE /api/v1/messages/{id}", historyAuth(http.HandlerFunc(s.handleDeleteMessage)))
 
 	// Realtime.
 	mux.HandleFunc("/ws/chat", s.handleWS)