fix: theme switching always defaults to dark mode

Root causes:
1. ThemeProvider was imported but never used in App.tsx and showSetupDialog
2. setThemeConfigCallbacks was never called to inject persistence callbacks
3. Preview/save/cancel theme lifecycle had no provider to coordinate

Changes:
- Export setThemeConfigCallbacks from @anthropic/ink
- Wrap App.tsx children with ThemeProvider (initialState from config, onThemeSave persists)
- Wrap showSetupDialog with ThemeProvider for onboarding/trust dialogs
- Call setThemeConfigCallbacks in init.ts to register load/save callbacks
- Update SnapshotUpdateDialog test to account for new ThemeProvider wrapper

Fixes #theme-switching

src/entrypoints/init.ts

@@ -20,7 +20,12 @@ import {
 import { preconnectAnthropicApi } from '../utils/apiPreconnect.js'
 import { applyExtraCACertsFromConfig } from '../utils/caCertsConfig.js'
 import { registerCleanup } from '../utils/cleanupRegistry.js'
-import { enableConfigs, recordFirstStartTime } from '../utils/config.js'
+import {
+  enableConfigs,
+  getGlobalConfig,
+  recordFirstStartTime,
+  saveGlobalConfig,
+} from '../utils/config.js'
 import { logForDebugging } from '../utils/debug.js'
 import { detectCurrentRepository } from '../utils/detectRepository.js'
 import { logForDiagnosticsNoPII } from '../utils/diagLogs.js'
@@ -51,6 +56,7 @@ import { setShellIfWindows } from '../utils/windowsPaths.js'
 import { initSentry } from '../utils/sentry.js'
 import { initUser } from '../utils/user.js'
 import { initLangfuse, shutdownLangfuse } from '../services/langfuse/index.js'
+import { setThemeConfigCallbacks } from '@anthropic/ink'
 
 // initialize1PEventLogging is dynamically imported to defer OpenTelemetry sdk-logs/resources
 
@@ -66,6 +72,11 @@ export const init = memoize(async (): Promise<void> => {
   try {
     const configsStart = Date.now()
     enableConfigs()
+    setThemeConfigCallbacks({
+      loadTheme: () => getGlobalConfig().theme,
+      saveTheme: setting =>
+        saveGlobalConfig(current => ({ ...current, theme: setting })),
+    })
     logForDiagnosticsNoPII('info', 'init_configs_enabled', {
       duration_ms: Date.now() - configsStart,
     })