feat(library): manga spec — jikan enrich, rss/mangadex chapter flip

tests/fixtures/canonical-manga.md

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+---
+type: manga_item
+title: Chainsaw Man
+eng_name: 
+read_status: Reading
+rating: 4
+rating_stars: ⭐️⭐️⭐️⭐️
+last_read_chapter: 210
+latest_chapter: 213
+last_chapter_date: 2026-07-16
+chapters: null
+volumes: null
+status: Publishing
+authors: ["Fujimoto, Tatsuki"]
+genre: [Action, Horror, Sports]
+score: 8.7
+published_from: 2018-12-03
+published_to: null
+mal_id: 116778
+mangadex_id: abc-123
+rss: "https://example.com/csm-feed.xml"
+poster: "https://cdn.myanimelist.net/images/manga/3/216464l.jpg"
+url: "https://myanimelist.net/manga/116778/Chainsaw_Man"
+tags: [mangas, manga]
+---
+
+# Chainsaw Man
+
+![poster|200](https://cdn.myanimelist.net/images/manga/3/216464l.jpg)
+
+**Manga** · Publishing · 8.7
+
+**Read Status:** Reading
+**Progress:** ch. 210 / 213
+
+## Synopsis
+Denji has been robbed of a normal life ever since his Chainsaw Devil, Pochita, merged with him.
+
+**Authors:** Fujimoto, Tatsuki
+
+## Links
+- [MAL page](https://myanimelist.net/manga/116778/Chainsaw_Man)
+- [RSS feed](https://example.com/csm-feed.xml)
+
+## My Notes
+