feat(media): reusable media management

Sprint 22.

- MediaAsset gains folder (flat) and MediaListParams gains folder/tag
  filters; MediaRepository.listFolders() derives the folder list from
  existing records
- upload validation: 10MB size cap, mime allow-list (jpeg/png/webp/gif/
  svg+xml/pdf), real error messages surfaced through MediaLibraryFacade
  instead of a generic swallowed string
- SVG uploads are sanitized (script tags and on*= attributes stripped)
  before storage
- raster images (excl. gif) are downscaled to a 2000px max dimension and
  re-encoded via canvas before storage - compression, not a crop UI
- tag editing (window.prompt, comma-separated) via
  MediaLibraryFacade.updateTags()
- MediaPickerComponent wired into Project Editor branding (logo, compact
  logo, favicon) alongside its existing category/product usage - confirmed
  no image fields exist on Static Pages or as a dedicated hero field to
  wire

docs/ADMIN.md updated with the new Sprint 22 section including the storage
abstraction note (MediaRepository was already the abstraction).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/project-editor/sections/section.shared.scss

@@ -11,6 +11,13 @@
   gap: 14px;
 }
 
+.media-field-row {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+}
+.media-field-row app-input { flex: 1; }
+
 .editor-grid {
   display: grid;
   gap: 12px;