web-ui: settings as inspector cards

[time-attack]

Summary

The settings page becomes a stack of inspector cards: Appearance (theme and
sidebar conversations as segmented controls, the theme file import as a text
link) and Account (sign-out as the header action; signed-in identity, admin and
about rows). Native selects and the menu-backed filter share one field box.

Demo

The Appearance card: switching Light / Dark / System and the sidebar conversations segments.

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	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 (this)	settings as inspector cards
9	#1061	selection actions toolbar
10	#1062	recommendation card

[time-attack]

Closing per review: holding off on importing Beautiful UI wholesale for now (interactions read as too stimulating and too Conductor-like). A subset may come back as our own take in collaboration with Eve. Branch bui/08-settings is kept.