fix(ebook-reader): load SVG images and fix progress update ID

- Add SVG image support: process <image xlink:href=...> elements
  in addition to HTML <img> tags for cover pages and embedded images
- Fix progress update: use 'id' from API response instead of
  'media_item_id' which the backend never returns for this endpoint
- Update reader context interfaces to include currentPage field
- Add debug logging for all resource keys to help troubleshoot
  image loading issues in future epubs

web/src/reader/core/reader-state.ts

@@ -1,4 +1,4 @@
-import type { ReaderMetadata, ReaderState } from "./reader-context";
+import type { ReaderState } from "./reader-context";
 
 type CurrentReader = import("./reader-context").CurrentReader;