move branding settings from Theme tab to Site tab

- Add branding_editor component to site_editor.ex with:
  - Shop name input
  - Show shop name / Show logo toggles
  - Logo upload (size slider, SVG recolor, color picker)
  - Header background toggle and upload (zoom, position sliders)
- Add site_ prefixed event handlers in page_editor_hook.ex:
  - site_update_branding, site_toggle_branding, site_update_color
  - site_remove_logo and site_remove_header (delegate to theme handlers)
- Remove branding sections from theme_editor.ex:
  - Deleted shop_name_input, branding_section, logo/header upload sections
- Theme tab now shows only: preset grid, accent colours, customise accordion

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PROGRESS.md

@@ -160,13 +160,13 @@ Restructure the 3-tab editor panel for better discoverability. Replace Settings
 | 8-9 | Social links editor (CRUD, reorder, platform detection, URL normalization) | 2h | done |
 | 10-14 | Header & footer navigation editors | 3h | done |
 | 15-16 | Footer content (about, copyright, newsletter toggle) | 1.25h | done |
-| 17-18 | Move branding from Theme to Site | 1.5h | planned |
+| 17-18 | Move branding from Theme to Site | 1.5h | done |
 | 19-20 | Merge page settings into Page tab, remove Settings tab | 1h | planned |
 | 21-22 | Polish and testing | 2h | planned |
 
 Social links now support 40+ platforms (grouped by category), auto-detect platform from pasted URLs (including deep links like `tg://` and `spotify:`), normalize bare domains to https://, preserve custom protocols, and filter empty URLs from shop display.
 
-Navigation editors support add/edit/delete/reorder for both header and footer nav items. Page picker dropdown allows linking to system pages (home, about, contact, etc.) or custom published pages. Items persist immediately on change.
+Navigation editors support add/edit/delete/reorder for both header and footer nav items. Page picker dropdown allows linking to system pages (home, about, contact, etc.) or custom published pages. Changes preview immediately with live update in the shop layout. Removed legacy /admin/navigation page — nav editing is now exclusively through the Site tab with live preview.
 
 ### Unified editor session ([plan](docs/plans/unified-editor-session.md)) — Complete