feat(settings): replicate the WorkBuddy appearance panel and dark theme (TODO 11)

Recover the WorkBuddy 5.8.3 appearance page from REA evidence (appearance-DMmhwsxq.css + tokens-Df-i-zsO.css): 44 recovered .appearance-* rules, scoped light/dark tokens, original geometry (panel [232,40,638,640], preview 634x317, grid 634x218.391, cards 118.797x79.188) and the two REA-exported preview images with provenance sha256.

Wire the panel into SettingsDialog with only the requested light/dark cards, add scoped tokens to the settings shell so the dark theme no longer renders a white window with near-white text, and verify with scripts/verify-appearance-settings.cjs (21 assertions: geometry, instant switch, cross-window sync, persistence, dark/light surface sampling with contrast >= 4.5, no renderer errors). Update the legacy nav/account/desktop appearance verifiers to the new .appearance-card selectors.

scripts/verify-account-menu.cjs

@@ -237,12 +237,12 @@ if (!process.versions.electron) {
     await wait('!document.querySelector(".ycode-account-menu")', 'menu closed after appearance click')
     await openSettings('appearance')
     observe(settings)
-    await wait('!!document.querySelector(".segmented")', 'appearance panel', settings)
-    check('外观 row opens the real appearance panel', await read(`[...document.querySelectorAll('.segmented__item')].map(node=>node.textContent)`, settings), ['浅色', '深色'])
-    check('appearance panel marks the current light theme', await read(`[...document.querySelectorAll('.segmented__item')].map(node=>[node.textContent,node.dataset.active])`, settings), [['浅色', 'true'], ['深色', 'false']])
+    await wait('!!document.querySelector(".appearance-panel")', 'appearance panel', settings)
+    check('外观 row opens the real appearance panel', await read(`[...document.querySelectorAll('.appearance-card')].map(node=>node.getAttribute('aria-label'))`, settings), ['浅色', '深色'])
+    check('appearance panel marks the current light theme', await read(`[...document.querySelectorAll('.appearance-card')].map(node=>[node.getAttribute('aria-label'),String(node.classList.contains('appearance-card--selected'))])`, settings), [['浅色', 'true'], ['深色', 'false']])
 
     await step('menu-dark-theme')
-    await clickText('.segmented__item', '深色', settings)
+    await mouseClick('[aria-label="深色"].appearance-card', settings)
     await wait(`document.documentElement.dataset.theme==='dark'`, 'main window receives dark theme')
     check('appearance row drives the shared theme', await read(`[document.documentElement.dataset.theme,localStorage.getItem('ycode:theme')]`), ['dark', 'dark'])
     await read(openMenu)
@@ -262,12 +262,12 @@ if (!process.versions.electron) {
     await wait('!document.querySelector(".ycode-account-menu")', 'menu closed after settings click')
     await wait('!!document.querySelector(".models-settings-panel")', 'models panel in the reused settings window', settings)
     check('设置 row reuses the native settings window', BrowserWindow.getAllWindows().filter(win => win !== main).length, 1)
-    check('设置 row lands on the models panel', await read(`!!document.querySelector('.models-settings-panel')&&!document.querySelector('.segmented')`, settings), true)
+    check('设置 row lands on the models panel', await read(`!!document.querySelector('.models-settings-panel')&&!document.querySelector('.appearance-panel')`, settings), true)
 
     await step('menu-light-restore')
     await read(`document.querySelector('[data-settings-tab="appearance"]').click()`, settings)
-    await wait('!!document.querySelector(".segmented")', 'appearance panel again', settings)
-    await clickText('.segmented__item', '浅色', settings)
+    await wait('!!document.querySelector(".appearance-panel")', 'appearance panel again', settings)
+    await mouseClick('[aria-label="浅色"].appearance-card', settings)
     await wait(`document.documentElement.dataset.theme==='light'`, 'main window receives light theme')
     check('light theme is restored through the same settings window', await read(`[document.documentElement.dataset.theme,localStorage.getItem('ycode:theme')]`), ['light', 'light'])
     const settingsId = settings.id