revert: remove unrequested agent-work UI polish

[kristofferremback]

Problem

#1957 was merged after a misunderstanding about which of two independent PRs Kris wanted. The intended outcome is the attachment filename fix in #1958, without the agent-work UI changes.

Solution

Revert merge commit 749e164d in full. The resulting tree matches main immediately before #1957; #1958 has been reopened as the separate requested change.

Test plan

• 105 focused frontend tests
• Full lint, monorepo typecheck, migration checks, Dockerfile checks, and OpenAPI check through the commit hook
• git diff --cached --check

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PR by Pi using GPT-5.6 Sol

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📥 Commits

Reviewing files that changed from the base of the PR and between 749e164 and fd644a4.

📒 Files selected for processing (12)

• apps/frontend/src/components/board/board-row-item.effects.test.tsx
• apps/frontend/src/components/timeline/agent-session-event.test.tsx
• apps/frontend/src/components/timeline/agent-session-event.tsx
• apps/frontend/src/components/timeline/live-session-effect-grid.tsx
• apps/frontend/src/components/timeline/session-effect-grid.tsx
• apps/frontend/src/components/trace/trace-step-list.test.tsx
• apps/frontend/src/components/trace/trace-step-list.tsx
• apps/frontend/src/components/trace/trace-step.test.tsx
• apps/frontend/src/index.css
• apps/frontend/src/lib/effect-links.test.tsx
• apps/frontend/src/lib/effect-links.tsx
• tests/browser/agent-effects.spec.ts

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