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/transactions/[id]/categorize/route.ts

@@ -201,7 +201,7 @@ export async function POST(
   if (is_business && body.account_override) {
     // Validate the account exists in the user's chart of accounts
     const { data: accountExists } = await supabase
-      .from('accounts')
+      .from('chart_of_accounts')
       .select('account_number, account_class')
       .eq('user_id', user.id)
       .eq('account_number', body.account_override)