[Fix] Simplify the right sidebar artifacts panel

[samzong]

Summary

Remove the fake Progress experience from the right sidebar and keep that panel focused on artifacts only. This avoids presenting model-generated checklist text and metadata as if it were real execution progress.

Type of change

• [Feat] new feature
• [Fix] bug fix
• [UI] UI or UX change
• [Docs] documentation-only change
• [Refactor] internal cleanup
• [Build] CI, packaging, or tooling change
• [Chore] maintenance

Why is this needed?

The existing Progress panel was not backed by a real progress system. It inferred steps from assistant text and mixed that with task metadata, which created misleading status signals in the UI.

What changed?

• Removed progress parsing, progress tab UI, and the unused shared progress type
• Removed obsolete progress locale strings
• Simplified the right sidebar to an artifacts-only panel with a tighter layout

Architecture impact

• Owning layer: shared / renderer
• Cross-layer impact: none
• Invariants touched from docs/architecture-invariants.md:
• The three-panel layout is a core product affordance
• The renderer owns UI state and presentation
• Why those invariants remain protected:
• The three-panel layout remains intact, and the change is limited to renderer presentation plus removal of an unused shared type

Linked issues

Closes #

Validation

• pnpm lint
• pnpm test
• pnpm build
• Manual smoke test
• Not run

Commands, screenshots, or notes:

pnpm check
pnpm typecheck

Screenshots or recordings

UI change in the right sidebar only. The panel now shows artifacts without the fake Progress section or task metadata card.

Release note

• No user-facing change. Release note is NONE.
• User-facing change. Release note is included below.

NONE

Checklist

• The PR title uses at least one approved prefix: [Feat], [Fix], [UI], [Docs], [Refactor], [Build], or [Chore]
• The summary explains both what changed and why
• Validation reflects the commands actually run for this PR
• Architecture impact is described and references any touched invariants
• Cross-layer changes are explicitly justified
• The release note block is accurate

[github-actions]

Hi @samzong,
Thanks for your pull request!
If the PR is ready, use the /auto-cc command to assign Reviewer to Review.
We will review it shortly.

Details

Instructions for interacting with me using comments are available here.
If you have questions or suggestions related to my behavior, please file an issue against the gh-ci-bot repository.