Add draft-only invoicing rules, send reminders, and time clock billing.

Restrict line item edits to draft invoices, auto-create drafts on clock-out,
and add sendReminderAt scheduling with dashboard due reminders.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/server/db/schema.ts

@@ -369,6 +369,7 @@ export const invoices = createTable(
     publicToken: d.varchar({ length: 255 }).unique(),
     publicTokenExpiresAt: d.timestamp(),
     lastReminderSentAt: d.timestamp(),
+    sendReminderAt: d.timestamp(),
     createdAt: d
       .timestamp()
       .default(sql`CURRENT_TIMESTAMP`)