web-ui: chat rows, session header and empty state

[time-attack]

Summary

User messages become the reference bubble on the field colour, assistant text
takes the 14 px / 1.55 body voice, the message footer is a 24 px action lane, and
the streaming tail fades words in without blur. The session header is a tab
strip — crumb as a ghost tab, title as the active pill, six 28 px tool buttons
with count badges — and the empty chat shows the 21 px headline. Read-only and
shared transcripts share the same bar.

Demo

Scrolling a conversation: the user bubble, assistant typography, the hover action lane, then the tab-strip header and the empty-state headline.

Verification

Typecheck, the full plugins/web-ui suite, eslint and prettier pass at this level of the stack (each level is verified on its own, on top of the previous one). Live QA of the finished stack ran in a browser-only dev-instance against a seeded conversation (tool run, markdown table, TypeScript and diff fences, a pending approval, ⌘K, list pages, settings), in light and dark and at phone width.

Stack

Merge in order; each PR is based on the one above it and retargets automatically when its base merges.

#	PR	Change
1	#1053	Beautiful UI foundation — tokens, fonts, styles scaffold
2	#1054	loading state and the live thinking trace
3	#1055 (this)	chat rows, session header and empty state
4	#1056	approval card with a pager
5	#1057	tool chips and code blocks
6	#1058	records tables and filter lists
7	#1059	search palette
8	#1060	settings as inspector cards
9	#1061	selection actions toolbar
10	#1062	recommendation card