add favicon and site icon generation from uploaded images

Upload a source image (PNG, JPEG, or SVG) and get a complete favicon
setup: PNG variants at 32, 180, 192, 512px served from DB via
FaviconController with ETag caching, SVG favicon for vector sources,
dynamic site.webmanifest, and theme-color meta tag. Theme editor gains
a site icon section with "use logo as icon" toggle, dedicated icon
upload, short name, and background colour picker.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PROGRESS.md

@@ -94,9 +94,9 @@ Plans: [admin-redesign.md](docs/plans/admin-redesign.md) | [admin-font-loading.m
 | ~~54~~ | ~~CSV export~~ | 52 | 1.5h | done |
 | ~~55~~ | ~~Entry/exit pages panel~~ | — | 1h | done |
 | | **Favicon & site icons** ([plan](docs/plans/favicon.md)) | | | |
-| 86 | Favicon source upload — `image_type: "icon"`, "use logo as icon" toggle, upload in theme editor, `FaviconGeneratorWorker`, `favicon_variants` table | — | 2.5h | planned |
-| 87 | `FaviconController` serving all favicon routes + dynamic `site.webmanifest`; `<link>` tags + `theme-color` meta in `shop_root.html.heex`; default fallback icons | 86 | 1.5h | planned |
-| 88 | SVG dark mode injection for SVG-source favicons; icon background colour + short name customisation | 86 | 1h | planned |
+| ~~86~~ | ~~Favicon source upload — `image_type: "icon"`, "use logo as icon" toggle, upload in theme editor, `FaviconGeneratorWorker`, `favicon_variants` table~~ | — | 2.5h | done |
+| ~~87~~ | ~~`FaviconController` serving all favicon routes + dynamic `site.webmanifest`; `<link>` tags + `theme-color` meta in `shop_root.html.heex`~~ | 86 | 1.5h | done |
+| ~~88~~ | ~~SVG dark mode injection for SVG-source favicons; icon background colour + short name customisation~~ | 86 | 1h | done |
 | | **No-JS support** | | | |
 | 56 | Audit all key flows for no-JS (browse, cart, checkout, analytics) | — | 2h | planned |
 | 57 | Fix any broken flows for no-JS clients | 56 | TBD | planned |