fix(vscode): improve composer mode selector layout

[hiarun02]

Description

Moves the VS Code chat composer mode selector next to the model dropdown and makes mode labels clearer. The mode selector now appears as a normal dropdown label, for example Auto-Accept, instead of a cramped/raw mode id near the send button.

Closes #1095

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Changeset

• Added a changeset (pnpm changeset) describing this change for the changelog

No changeset added because this is a small VS Code extension UI polish change.

Testing

Automated Tests

• New features include passing tests in .spec.ts/tsx files
• All existing tests pass (pnpm test:all completes successfully)
• Tests cover both success and error scenarios

Ran:

• ./node_modules/.bin/ava source/vscode/chat-panel-*.spec.ts
• ./node_modules/.bin/tsc --noEmit

Manual Testing

Attached proof video showing:

• Mode selector appears next to the model dropdown
• Mode selector uses readable labels like Auto-Accept
• Dropdown opens and mode switching still works
• Send button remains separated on the right

screen.mov

Checklist

• If this was for an open issue, I was assigned to it
• Code follows project style guidelines
• Self-review completed
• Documentation updated (if needed)
• No breaking changes (or clearly documented)
• Appropriate logging added using structured logging (see CONTRIBUTING.md)

No logging changes were needed because this is a UI-only change.

[github-actions]

No changeset found

This PR does not add a changeset, so it will not appear in the changelog or trigger a release.

If the change is user-facing, add one:

pnpm changeset

Pick a bump (patch / minor / major) and write the changelog entry in our usual voice ("Added X... Thanks to @you. Closes #123."), then commit the generated .changeset/*.md file.

If this PR is docs-only or a chore that needs no release note, you can ignore this - or run pnpm changeset --empty to record that intentionally.