merge page settings into Page tab and remove Settings tab

Custom page settings (title, slug, meta, published, navigation) now
appear as a collapsible section at the top of the Page tab. The
separate Settings tab has been fully removed.

- Add page_settings_section component to page_renderer.ex
- Remove dead :settings case from editor_panel_content
- Delete settings_editor.ex component entirely
- Remove SettingsEditor import from shop_components.ex
- Add .page-settings-* CSS styles
- Clean up old .settings-* CSS styles

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

PROGRESS.md

@@ -161,9 +161,11 @@ Restructure the 3-tab editor panel for better discoverability. Replace Settings
 | 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 | done |
-| 19-20 | Merge page settings into Page tab, remove Settings tab | 1h | planned |
+| 19-20 | Merge page settings into Page tab, remove Settings tab | 1h | done |
 | 21-22 | Polish and testing | 2h | planned |
 
+Custom page settings (title, slug, meta description, published, navigation options) now appear inline in the Page tab as a collapsible section. The separate Settings tab has been fully removed along with the SettingsEditor component.
+
 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. 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.