Problem: Form POST to same page required PHP session + page re-render.
Save appeared to work but values weren't persisting to Supabase reliably.

Fix: Save button now POSTs to /api/branding.php directly as JSON.
- Collects all input values from DOM
- Sends { action: 'save_theme', values: { key: value, ... } }
- API writes each value to platform_theme table (upsert)
- No session dependency, no form submission, no page reload
- Response confirms success/failure with message

On page refresh: PHP reads from platform_theme → shows saved values ✅Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>