fix: extend CORS origins to comix and kagane, preserve progress on unparseable chapters

- .env.example, DEPLOY.md, docker-compose.yml: add comix.to/kagane.to to
  ALLOWED_ORIGINS so the userscript isn't CORS-blocked on either new site
- .env.example: comment out BROWSER_WS_URL's DNS-name default, which
  overrides the working compose default and 500s Chrome's DevTools handler
- userscript: updateToCurrentChapter() now falls back to the stored
  chapter/label when chapterNum is unparseable, instead of wiping progress
  (kagane's og:title lacks a number when a chapter has no episode suffix)
- README.md: document comix/kagane in the config table, adapter reference,
  and key examples

userscript/manga-bookmark.user.js

@@ -838,8 +838,8 @@
       title: existing.title || p.title || p.seriesId,
       series_url: existing.series_url || p.seriesUrl || "",
       cover: existing.cover || p.cover || "",
-      last_chapter: p.chapterLabel || "",
-      last_chapter_num: p.chapterNum,
+      last_chapter: p.chapterLabel || existing.last_chapter || "",
+      last_chapter_num: p.chapterNum != null ? p.chapterNum : existing.last_chapter_num,
       last_chapter_url: p.chapterUrl || "",
       updated_at: Date.now(),
     });