refactor(reader): serve pages as static files instead of base64

Replace the per-page API call (base64 payload) with static image URLs
served directly by Caddy from public/images/pages/{chapterId}/.

- LocalImageStorage now stores to public/images/ (was MANGA_DATA_PATH)
- LegacyChapterRepository returns /images/pages/{id}/{file} URLs,
  uses getimagesize() instead of loading file content into memory
- Delete GetChapterPage query/handler/response, ChapterPageResource,
  ChapterPageProvider, PageContent model
- Remove getPageContent() from ChapterRepositoryInterface
- Frontend: loadChapter() fetches chapter + all pages in parallel,
  ReaderPage uses URL instead of base64 data URI, InfiniteReader drops
  lazy-load observer side effect, readerStore drops loadedPages/preload
- GetChapterPagesTest: extract fixture images from CBZ at runtime,
  ignore tests/Fixtures/pages/ in .gitignore

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

.gitignore

@@ -38,3 +38,4 @@ yarn-error.log
 /public/images/
 src/Controller/TestController.php
 .phpunit.cache/test-results
+/tests/Fixtures/pages/