Redesign Billing Page with Products Tabs

Redesign Plan & Billing (/org/billing): - Redesign to Standard style/colors/controls with tabs, tables, etc - Merge Plan + Billing. Menu: Billing - Tabs: - Products tab: - minimalistic table style with key info - clicking leads to an edit page - current subscription with Change button - Any additional products: nodes with storage, AI, etc. - Jaah AI product only if subscribed - shows balance and usage. Clicking on it leads to Jaah AI tabbed page - Add Product button - select Subscription (if not yet subscribed), Hosting, Jaah AI - Payment History - invoices - Payment Methods - Billing Details - Rename "Rental" to Hosting everywhere

Billing is now one tabbed page (Products/Payment history/Payment methods/Billing details) with subscription, hosting and Jaah AI sub-pages; Plan merged in (admin-only); Rental→Hosting renamed. Full gate + CI green; PR #4563 merged.