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/invoices/[id]/mark-paid/__tests__/route.test.ts

@@ -13,6 +13,10 @@ vi.mock('@/lib/supabase/server', () => ({
   createClient: () => Promise.resolve(mockSupabase),
 }))
 
+vi.mock('@/lib/init', () => ({
+  ensureInitialized: vi.fn(),
+}))
+
 const mockCreateInvoicePaymentJournalEntry = vi.fn()
 const mockCreateInvoiceCashEntry = vi.fn()
 vi.mock('@/lib/bookkeeping/invoice-entries', () => ({

app/api/invoices/[id]/mark-paid/route.ts

@@ -5,8 +5,11 @@ import {
   createInvoiceCashEntry,
 } from '@/lib/bookkeeping/invoice-entries'
 import { MarkInvoicePaidSchema } from '@/lib/api/schemas'
+import { ensureInitialized } from '@/lib/init'
 import type { EntityType, Invoice } from '@/types'
 
+ensureInitialized()
+
 /**
  * POST /api/invoices/[id]/mark-paid
  *

app/api/invoices/[id]/mark-sent/route.ts

@@ -1,8 +1,11 @@
 import { createClient } from '@/lib/supabase/server'
 import { NextResponse } from 'next/server'
 import { createInvoiceJournalEntry } from '@/lib/bookkeeping/invoice-entries'
+import { ensureInitialized } from '@/lib/init'
 import type { EntityType, Invoice } from '@/types'
 
+ensureInitialized()
+
 /**
  * POST /api/invoices/[id]/mark-sent
  *