T23b: AI chat, citations

- CitationBadge: a numbered pill after a claim, its source on hover, a press
  opens it; a Tab stop
- SourceCard and SourceList: the sources folded under their count and sites,
  each a card numbered as cited; the fold opens from the keyboard
- SearchProgress: steps waiting, working and done
- WebResultCard and DocumentChunkPreview with matched words washed
- gallery: citation and sources states

tasks/ch21-30.md

@@ -112,12 +112,12 @@
 
 ## T23b AI Chat · Citations
 
-- [ ] CitationBadge / InlineCitation
-- [ ] SourceCard
-- [ ] SourceList / SourcesPanel
-- [ ] SearchProgress
-- [ ] WebResultCard
-- [ ] DocumentChunkPreview
+- [x] CitationBadge / InlineCitation → `chat::CitationBadge`, set after the words it cites
+- [x] SourceCard
+- [x] SourceList / SourcesPanel → `chat::SourceList`
+- [x] SearchProgress
+- [x] WebResultCard
+- [x] DocumentChunkPreview
 
 ## T23c AI Chat · Input