Implements Phase 6 of Stripe billing integration:
- Add Billing tab to organization settings page
- Display subscription status, device usage, and estimated costs
- "Upgrade to Paid Plan" button for free tier orgs
- "Manage Billing" button to access Stripe Customer Portal
- Billing information panel showing subscription details
- Support for dark mode and responsive design
Also fixes organization name truncation in top navigation:
- Long organization names now show with ellipsis instead of being cut off
- Added max-w-xs constraint and truncate class to org switcher button
Graham McIntire
4b4bb2668f