fix: downgrade missing extension env vars to warning, add error boundaries and cron auth fixes

- Change missing extension env vars from throw to log.warn (graceful degradation)
- Move initialized flag after all init steps complete
- Add error.tsx and loading.tsx for dashboard error boundaries
- Fix cron route auth header checks
- Add ensureInitialized() to journal entry reverse and invoice mark-paid/sent routes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/api/extensions/enable-banking/sync/cron/route.ts

@@ -21,7 +21,7 @@ export async function GET(request: Request) {
   const authHeader = request.headers.get('authorization')
   const cronSecret = process.env.CRON_SECRET
 
-  if (cronSecret && authHeader !== `Bearer ${cronSecret}`) {
+  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
     return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
   }