feat(listing): populate Tags and CategorizedTags from figure data-tags

FA's beta listing pages emit each submission's tag list on the
figure's <img data-tags="..."> attribute, mixing prefixed system tags
(s_/c_/a_/u_/t_) with the unprefixed keyword list. Reading it during
gallery-page parse lets callers classify favorites/gallery/scraps/
browse/search/inbox items at scrape time, avoiding a /view/{id}
round-trip per submission.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

submission.go

@@ -35,10 +35,19 @@ type Submission struct {
 	Gender          Gender
 	Description     string // raw HTML; sanitise before rendering to a browser
 	DescriptionText string // plaintext convenience
-	Tags            []string
+	// Tags holds the user-supplied keyword tags. On /view/-path Submissions
+	// these come from div.submission-tags anchors. On listing-path
+	// Submissions (Gallery/Scraps/Favorites/Browse/Search/SubmissionInbox)
+	// they come from the figure's data-tags attribute, which carries the
+	// same keywords FA renders on /view/ for that submission.
+	Tags []string
 	// CategorizedTags groups FA's prefixed system tags by category.
-	// FA emits these as tag-block entries inside div.submission-tags with
-	// prefixes s_ (species), c_ (character), a_/u_ (artist), and t_ (type).
+	// On /view/-path Submissions FA emits these as tag-block entries inside
+	// div.submission-tags with prefixes s_ (species), c_ (character),
+	// a_/u_ (artist), and t_ (type). On listing-path Submissions the same
+	// prefixed tokens are parsed out of the figure's data-tags attribute;
+	// the a_ vs u_ distinction is lost there because FA collapses both into
+	// u_ in that flat list.
 	CategorizedTags CategorizedTags
 	FileURL         string // absolute CDN URL; pass to Download
 	ThumbURL        string