feat(cards): UserCard gets CardBox accent + drop dead approval-card type

[esengine]

Summary

Two small, related card-stream cleanups discovered while auditing visual consistency after #140.

1. UserCard → CardBox

Of the cards that render <Markdown> (variable-length, wrap-prone content), StreamingCard and ReasoningCard use CardBox so the ▎ left bar continues across wrap continuations. UserCard was the odd one out — long pasted prompts wrapped without an accent and lost rhythm against the now-accented model output. Bringing it in line uses CARD.user.color (FG.meta / dim slate) — deliberately quieter than the brand-toned streaming bar so user prompts don't compete visually with model replies.

The other 13 cards already get a per-line ▎ via BarRow/CardHeader; they pre-clip with clipToCells so wrap-continuation isn't a concern. They stay as-is.

2. Drop dead approval card kind

src/cli/ui/state/cards.ts:160 declared an ApprovalCard interface with kind: "approval" and routed it through the Card union. Audit:

• Zero producers in src/ or tests/
• The CardRenderer case routed to FallbackCard ("approval card · not yet migrated")
• The actual approval UI (EditConfirm / ShellConfirm / PlanConfirm) is built on the unrelated ApprovalCard.tsx modal HOC — name collision, but no wire-up

Per CLAUDE.md ("certain something is unused → delete it completely"). Removed: the interface, the union member, the orphan case "approval". CardRenderer's default branch still catches any future card kind safely.

Test plan

• npm run verify — 1829/1829 tests pass (PR fix(code): normalize edit replacements to target line endings #142's 5 new ones included)
• Visual: long user prompt now shows continuous ▎ accent against model reply's brand bar
• CI green

Out of scope

• Migrating BarRow-using cards to CardBox — they pre-clip, no wrap-continuation gap
• Full-width background highlight (lamyc RFC RFC · CLI / TUI design + interaction — what works, what is missing, what would you change? #20 literal ask) — would need per-line <Text backgroundColor> wrapping; separate RFC if pursued
• LiveCard accent — single-row status indicator; bar would be visual noise

Refs

• RFC discussion RFC · CLI / TUI design + interaction — what works, what is missing, what would you change? #20 — readability ask
• PR feat(cards): left accent bar on done assistant replies #126 — original brand accent on done assistant
• PR fix(tui): redesign reasoning + streaming cards #136 — card redesign / CardBox extraction
• PR fix(cards): restore brand accent on done-state assistant reply #140 — restored brand color on done state