fix(mobile-web): unify transcript card spacing and collapsed heights

[bobleer]

Summary

Unify mobile chat task/tool cards and todo cards with 12px corners, 12px horizontal padding, aligned icon/text columns, and 48px collapsed row heights including borders. Add space between consecutive cards and soften error outlines so failed tasks do not dominate the transcript.

Todo headers now remain left-aligned, retain a label when expanded or idle, and expose their expanded state and associated list to assistive technology. Bound progress dots and agent labels on narrow screens, preserve visible keyboard focus, and respect reduced motion for activity indicators.

Type and Areas

Type: Bug fix / UI/UX

Areas: Mobile web chat transcript

Motivation / Impact

Transcript overrides previously removed all horizontal padding and reduced rows to 36px, while prominent task cards independently used 16px corners. Icons touched card edges, adjacent failures crowded together, and todo/task/disclosure rows had inconsistent geometry. These changes establish consistent spacing and collapsed heights using existing theme tokens.

Verification

Passed:

• pnpm --dir src/mobile-web run test:ui-components (15 tests)
• pnpm --dir src/mobile-web run type-check
• pnpm run theme:color-audit:all
• pnpm run build:mobile-web (existing large-chunk warning)
• git diff --check

Manual visual checks in the Codex in-app browser using the actual React transcript components with synthetic host payloads: 320/375/414/768px layouts, dark/light themes, todo expansion, keyboard focus, and running/completed/failed/pending task presentation. Browser geometry inspection confirmed 48px collapsed todo, task, thinking, and grouped-read rows. The temporary preview files are excluded from the PR.

Reviewer Notes

Presentation-only changes; no transport, persisted data, or protocol changes. Remote control rendering was exercised locally with synthetic payloads, not an actual connected remote host. Remote workspace, live remote control, Peer Device Mode, and Detached Dispatch were not exercised end to end.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable (reuses the existing localized todo label).