Subscription panel, promo codes, and a real Talk-to-sales flow
Three additions on top of the pricing refresh:
1. /billing now shows your current subscription at the top — plan, status, days until renewal, recent invoices, and a one-click cancel that preserves access to end-of-period.
2. Promo codes. /billing has a "Have a promo code?" expander; apply a code and Pro plan cards instantly show the discounted price. Admin can create / edit / time-window codes at /admin/coupons (percent off, fixed INR, or fixed USD; per-plan scope; max redemptions; per-user limit).
3. Dedicated /contact-sales form for Team and Enterprise inquiries. Captures name, email, company, team size, use case and phone, emails our sales inbox, and shows up at /admin/leads with a kanban-style status (new → contacted → qualified → won/lost) plus staff notes.
Migration 014 adds three tables (coupons, coupon_redemptions, sales_leads).