fix: sheet Escape & focus management, detail a11y, 44px touch targets

- AppSheet: Escape closes any sheet branch; non-modal/inline sheets move
  focus into panel on open; modal<->inline transition keeps overlay stack
- Task detail: initial focus on close button; note textarea aria-label
- Global sr-only status region for toast announcements (visual toast hidden
  from AT to avoid double reading)
- Focus view: drop duplicate topbar h1 (page keeps its own single h1)
- Archived lists toggle hidden until loaded (no more 'archived 0' flash)
- Touch: date-clear/time-remove 44px; edit/preview switch hit area 44px
  with 3px gap; calendar filter row gets a scroll-right mask hint

frontend/src/style.test.ts

@@ -160,7 +160,7 @@ describe('approved Settings 01 paper ledger', () => {
   it('moves Settings identity into the body and suppresses the duplicate shell title', () => {
     expect(app).not.toContain("'settings-main':activeView==='settings'")
     expect(app).toContain(":class=\"{'settings-topbar':activeView==='settings'}\"")
-    expect(app).toContain("v-if=\"!['today','tasks','upcoming','trash','habits','settings'].includes(activeView)\" class=\"topbar-title\"")
+    expect(app).toContain("v-if=\"!['today','tasks','upcoming','trash','habits','settings','focus'].includes(activeView)\" class=\"topbar-title\"")
     expect(app).not.toContain('v-if="activeView===\'settings\'" class="icon topbar-refresh settings-refresh"')
     expect(app).not.toContain('aria-label="刷新当前页面"')
     expect(mvpPanel).toContain('<header class="settings-heading"><h1>设置</h1><p>管理数据、账户与登录设备</p></header>')