feat(web): terminal material — cctrace's design language, ccx's bones

[lroolle]

Summary

Eric's verdict: cctrace's session UI is the taste reference; ccx web's "color/font, layouts, interactions, details are looking bad". This ports cctrace's design language onto ccx's existing markup — every selector and JS hook kept, values rewritten — so the diff is a material swap, not a rewrite. Second commit ports cctrace's clamp mechanic.

• Type: 13px ui-monospace body (was 17px system sans; 'Courier New' led the old mono stack), 10/11/12/13 sub-scale, 18px page h1
• Palette: warm-tinted neutrals (kiln: tint neutrals toward brand hue — light #fcfbfa, dark #131110), terracotta as the single accent (deepened to #c65d3e light / #e08662 dark for contrast), and a five-hue semantic set (green/red/amber/purple/blue). All ~12 stray hues (#e9a, #a80, #5a9, #fa0, #d55, #86c, blue/violet/cyan context accents...) collapsed onto tokens
• Surfaces: pastel role bubbles → hairline material with faint washes; user turns get cctrace's anchor mechanic (extra space above + accent-washed header row in a hairline box); thinking becomes muted italic
• Interactions: long tool outputs clamp with a fade mask + explicit "show all" expander instead of an inner scrollbar — the wheel never gets trapped inside a pane. Progressive enhancement: panes inside collapsed details clamp lazily on first open; no JS = old scroll behavior
• Side-stripe purge round 2 (kiln permanent anti-pattern; the 0.11 pass missed these): tool blocks (2px blue), outline active item (2px cyan), agent turns (2px purple), doctor/memory/settings cards (3px)
• Chrome: thin scrollbars, accent selection, :focus-visible outlines, two tinted shadow tokens, radius scale 6/4/999
• Correctness detail: uppercase role labels exempt command names and agent types (/init must not render /INIT)

Deliberate choice: terracotta stays the accent rather than copying cctrace's GitHub blue — the badness was hue-scatter + pastels, not the brand hue, and warm neutrals under a warm accent keep ccx's identity instead of cloning cctrace. Rationale + decision table in docs/devlog/2026-07-29-web-terminal-material.org.

Follow-up candidates (not in this PR): replay transport, tabular-nums pass on stat rows.

Will trivially conflict with #26/#28 on the CHANGELOG [Unreleased] header — keep all entries.

Test plan

• go build ./... clean, go test ./... green (web tests cover template rendering)
• Live smoke: ccx web served the sessions index and the f8e49d74 session view at 200; served HTML carries the new tokens, the turn-user/turn-role markup the new rules target, and the clamp module
• Visual review is host-gated (no browser in the deva container) — screenshots on Eric's side

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