ui: context menus and the title-bar menus on the kit's menu surface (#1465) #1732

Part of #1465 (step 4a).

Problem

Right-click menus and the window menu bar are shadcn widgets while every other menu (dropdowns, split and menu buttons) is the kit's MenuAnchor surface (querya_menu_surface.dart, queryaMenuItems). Uses on dev (2026-10-18): MenuButton 114, ContextMenu 15, MenuDivider 15, MenuItem 13, showContextMenuBuilder 1, Menubar 1.

Where:

• connection tree context menus (features/connections, ~45 entries: Postgres / MySQL / SQLite / Mongo / Redis / extension trees, folders, sidebar)
• window title bar menus File / Edit / View / Connection / Help (querya_window_title_bar.dart, Menubar + 30 entries)
• ERD card and group menus (erd_table_menu.dart, erd_group_menu.dart, ~24)
• result grid cell menu (grid_cell_actions.dart, showContextMenuBuilder, ~15)

The two menu styles look and behave differently (padding, hover, keyboard, submenu arrow), so the same app has two kinds of menus.

Change

• QueryaContextMenu (wraps a child, opens on secondary tap / long press / context-menu key at the pointer) and a menu entry model with submenu, divider, shortcut hint and disabled state, all on the kit's menu surface.
• QueryaMenuBar for the title bar on the same surface (keyboard: Alt / F10 opens, arrows move between menus).
• Migrate the four areas above, one PR each if it gets big; keep every ValueKey the tests use.
• Guard: no ContextMenu, MenuButton, MenuDivider, MenuItem, Menubar, showContextMenuBuilder from shadcn in lib/.

Acceptance

• All context menus and the menu bar use the kit; the guard passes.
• Keyboard: menus open with the context-menu key / Shift+F10, arrows and Esc work, submenus open with Right.
• Widget tests for open / select / submenu / Esc; existing menu tests pass with their keys.