remove the onboarding flow and the accountMode leftover

Onboarding was dead in three layers:

- The OnboardingAdmin screen was only reachable from a route block in App.tsx
  that has been commented out, so it never rendered. Its ServerTypeCard carried
  accountMode ('organization' | 'single'), inherited from the codebase this was
  based on and meaningless for a single-user platform.
- Two /onboarding-complete endpoints, one public and one protected, that no
  frontend code called. Both read a server_config key that was never written, so
  both answered false while the app's own path defaulted to true.
- HomeScreen gated on settings.onboarding.complete to show a welcome panel, and
  seedHomeDir created an Onboarding folder from DATA_PATH/Onboarding and
  /Onboarding_Admin — neither seed directory exists, so it only ever produced an
  empty folder.

Also drops the onboarding key from UserSettings and the now-empty home-header
panel from the default home layout.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/hono.ts

@@ -67,11 +67,6 @@ honoServer.post('/api/hooks/claude-done', async (ctx) => {
   }
   return ctx.json({ ok: true });
 });
-honoServer.get('/api/server-settings/onboarding-complete', async (ctx) => {
-  const { readServerSettings } = await import('officerdb');
-  const settings = await readServerSettings();
-  return ctx.json({ onboardingComplete: !!settings.onboardingComplete });
-});
 
 const protectedRouter = createRouter();
 protectedRouter.use(bodyParser());