feat: add recurring invoices, public links, time tracker, payments, reminders

- Recurring invoices: schedule-based auto-generation with CRUD UI at /dashboard/invoices/recurring and POST /api/cron/generate-recurring cron endpoint
- Public invoice link: generate/revoke shareable /i/[token] page for unauthenticated clients with PDF download
- Live time tracker: localStorage-persisted timer widget in invoice editor that appends a line item on stop (rounds to nearest 0.25h)
- Partial payment tracking: record payments per invoice, auto-mark paid when fully covered, balance due display
- Send reminder: email reminder via Resend with custom message dialog and last-sent indicator

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

src/components/forms/invoice-form.tsx

@@ -805,6 +805,8 @@ export default function InvoiceForm({ invoiceId }: InvoiceFormProps) {
                   onRemoveItem={removeItem}
                   onUpdateItem={updateItem}
                   onAddItemWithValues={addItemWithValues}
+                  invoiceId={invoiceId && invoiceId !== "new" ? invoiceId : undefined}
+                  defaultRate={formData.items[0]?.rate}
                 />
               </CardContent>
             </Card>