web-ui: loading state and the live thinking trace

[time-attack]

Summary

Loading: a 3×3 pixel-grid loader replaces the wave loader on the chat surface,
the working label shimmers, and the live status above the composer shows the
elapsed time of the current tool. Thinking: the streaming assistant row renders
the reference Thinking trace — open while the run is active with a shimmering
"Thinking" / "Searching the web" / "Running tools" header, reasoning
paragraphs, tool rows and search results fading up onto a guide line as they
arrive — and settles to a collapsed "Thought for Ns" / "Searched the web" /
"Ran N tools" header. Tool rows gain the compact label + mono detail layout
the trace relies on. Restores upstream's sandbox tool categorisation helpers in
the timeline so unified sandbox calls keep their labels and output.

Demo

First: the pixel-grid loader, shimmer label and elapsed counter while a command runs. Second: the trace opens live with "Thinking" then "Running tools", tool rows fade in as they run, and it settles to "Thought for Ns" / "Ran 4 tools".

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 (this)	loading state and the live thinking trace
3	#1055	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