feat(query): sql workspace conveniences per opsxdb patterns

- generic ContextMenu component (viewport flip, esc/outside close)
- SchemaSidebar table right-click menu: preview data, generate
  SELECT/INSERT/UPDATE/DELETE templates with pk-aware WHERE, copy table
  name; double-click table runs preview SELECT; column right-click
  copy/insert; dialect-aware quoting; preview SELECT carries no LIMIT
- SqlEditor selection-first execution (Mod-Enter runs selection else
  statement at cursor via quote/comment-aware splitter); pagination
  replays last executed statement
- query history persisted server-side: drawer fetches query-histories
  with keyword/mine/favorites filters, star toggle (new PUT favorite +
  mine filter endpoints), insert and insert-and-run
- custom templates in localStorage alongside built-ins
- unit tests: genSql + statement splitter (28 tests green)

backend/router/router.go

@@ -199,6 +199,7 @@ func Setup(r *gin.Engine) {
 		}
 		auth.GET("/announcements", handler.ListAnnouncements)
 		auth.GET("/query-histories", handler.ListQueryHistories)
+		auth.PUT("/query-histories/:id/favorite", handler.ToggleQueryHistoryFavorite)
 		// Notifications CRUD (replaces old channels/templates endpoints)
 		auth.GET("/notifications", handler.ListNotifications)
 		auth.POST("/notifications", handler.CreateNotification)