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.md

@@ -73,7 +73,7 @@ Per-component lines live in `tasks/`. Tags there:
 - [x] T21c Documents · Knowledge
 - [x] T22 Collaboration
 - [x] T23a AI Chat · Messages
-- [ ] T23b AI Chat · Citations
+- [x] T23b AI Chat · Citations
 - [ ] T23c AI Chat · Input
 - [ ] T23d AI Chat · Conversations
 - [ ] T23e AI Chat · Welcome