feat(frontend): add invoice dashboard with status filtering and reminders (Closes #602)

[waterWang]

Summary

Builds the invoice dashboard (issue #602) on top of the existing invoice components
(InvoiceCard / InvoiceDetail / InvoiceModal), which previously had no list page, no
persistence, and no reminders:

• lib/invoices.ts — full localStorage-backed invoice store (same pattern as lib/paymentLinks.ts):
  • loadInvoices() / saveInvoices() with SSR guard + corrupt-data fallback
  • createInvoice() — generates id, sequential INV-00001 numbering, default draft status
  • updateInvoiceStatus() / deleteInvoice() — persisted mutations
  • sendInvoiceReminder() — mailto: hand-off (works with any mail client, no server infra) + records lastReminderAt
  • summarizeInvoices() — per-status + grand totals, with an "outstanding" (sent + overdue) figure
  • generateInvoicePDF() — jsPDF invoice PDF (same stack as existing receipts)
• pages/invoices.tsx — the /invoices dashboard (previously a "coming soon" placeholder):
  • Status filter tabs (All / Draft / Sent / Paid / Overdue) with per-status counts
  • Summary cards for Outstanding / Paid / Total
  • "New Invoice" → InvoiceModal; "View Details" → InvoiceDetail overlay
  • Deep-link support via ?invoice=<id> (shareable detail URLs)
  • Reminder action per invoice via mailto: + toast confirmation
• components/Navbar.tsx — adds the Invoices nav link
• i18n — invoices.* keys + nav.invoices added to all 7 locale files (en/es/fr/pt/ja/ar/he)
• Tests — 11 unit tests for the store (invoices-lib.test.ts) + 7 component tests for the page
  (InvoicesPage.test.tsx): empty state, list + summary, status filtering, deep-link detail,
  open-detail-on-click, reminder flow, filtered empty state
• Storybook — InvoicesPage.stories.tsx (default populated list, empty state)

Verification

• NODE_ENV=test npx jest __tests__/invoices-lib.test.ts __tests__/InvoicesPage.test.tsx → 18/18 pass
• tsc --noEmit — only pre-existing lib/sdk-instance.ts errors (TS1127/TS1160, introduced by
  PR#918 on main, unrelated to this change)

Closes #602

Signed-off-by: waterWang water.wang@users.noreply.github.com

[Topmatrixmor2014]

PLEASE FIX CONFLICTS