feat: add frosted glass appearance and improve local MCP recovery

Add an opt-in persistent frosted glass setting for the top bar and runtime checklist, with chat scrolling behind the header while preserving scroll anchors and window controls.

Retry transient local MCP initialization failures once after cleanup, include redacted connection diagnostics in feedback, and index lifecycle events to reduce execution statistics scans.

Release note: Add optional frosted glass appearance with chat visible behind the title bar; improve local tool connection recovery and diagnostic feedback.

src/renderer/src/SettingsPanel.tsx

@@ -235,6 +235,12 @@ type SettingsPanelProps = {
   onExpertsChanged?: (experts: AssistantExpert[]) => void
   onClearLocalData: () => Promise<void>
   appearanceTheme?: AppearanceTheme
+  transparentFrostedEffectEnabled?: boolean
+  applicationSettingsPending?: boolean
+  applicationSettingsLocked?: boolean
+  applicationSettingsError?: string
+  onTransparentFrostedEffectEnabledChange?: (enabled: boolean) => Promise<boolean>
+  onRetryApplicationSettings?: () => void
   onAppearanceThemeChange?: (theme: AppearanceTheme) => void
   brandingPreferences?: BrandingPreferences
   brandingFallbackLogo?: string
@@ -648,6 +654,12 @@ export function SettingsPanel({
   onClearLocalData,
   onExpertsChanged = () => {},
   appearanceTheme = 'system',
+  transparentFrostedEffectEnabled = false,
+  applicationSettingsPending = false,
+  applicationSettingsLocked = false,
+  applicationSettingsError,
+  onTransparentFrostedEffectEnabledChange,
+  onRetryApplicationSettings,
   onAppearanceThemeChange = () => {},
   brandingPreferences = defaultBrandingPreferences,
   brandingFallbackLogo,
@@ -2340,6 +2352,32 @@ export function SettingsPanel({
                   )}
                 </div>
               </div>
+              <div className="settings-section">
+                <label className="toggle-row">
+                  <span>{t('appearance.frostedGlass.label')}</span>
+                  <input
+                    type="checkbox"
+                    role="switch"
+                    checked={transparentFrostedEffectEnabled}
+                    disabled={applicationSettingsPending || applicationSettingsLocked || !onTransparentFrostedEffectEnabledChange}
+                    aria-describedby="frosted-glass-description"
+                    onChange={(event) => {
+                      void onTransparentFrostedEffectEnabledChange?.(event.target.checked)
+                    }}
+                  />
+                </label>
+                <p id="frosted-glass-description" className="settings-panel__description">
+                  {t('appearance.frostedGlass.description')}
+                </p>
+                {applicationSettingsError && (
+                  <div role="alert">
+                    <p>{applicationSettingsError}</p>
+                    <button className="secondary-button" disabled={applicationSettingsPending} onClick={onRetryApplicationSettings} type="button">
+                      {t('appearance.frostedGlass.retry')}
+                    </button>
+                  </div>
+                )}
+              </div>
               <div className="settings-section appearance-settings">
                 <div className="settings-section__title">
                   <span className="inline-help-label">