feat(chat): add previous checkpoint navigation controls and i18n

[saneroen]

Use this PR body with issue linked to #12138:

Related GitHub Issue

Closes: #12138

Roo Code Task Context (Optional)

N/A

Description

Adds previous-checkpoint navigation in chat so users can quickly revisit earlier checkpoints in long conversations.

• Adds a footer action to jump through prior checkpoints.
• Wires checkpoint menu jump callback support.
• Adds/updates tests for checkpoint navigation behavior.
• Adds chat:scrollToLatestCheckpoint locale key across chat locale files.

Test Procedure

From webview-ui:

1. Run lint:
   • pnpm run lint
2. Run targeted tests:
   • npx vitest run src/components/chat/__tests__/ChatView.scroll-debug-repro.spec.tsx
   • npx vitest run src/components/chat/checkpoints/__tests__/CheckpointSaved.spec.tsx
3. Manual verification:
   • Open a task with checkpoints.
   • Confirm checkpoint jump button appears when checkpoints exist.
   • Click repeatedly and verify it navigates to earlier checkpoints.
   • Click scroll-to-bottom and verify jump cursor resets.

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue.
• Scope: Changes are focused on the linked issue.
• Self-Review: Code self-review completed.
• Testing: New/updated tests cover the change.
• Documentation Impact: No user-doc updates required.
• Contribution Guidelines: Reviewed CONTRIBUTING.md.

Screenshots / Videos

UI change present; attach screenshot/video from local verification.

Documentation Updates

• No documentation updates are required.
• Yes, documentation updates are required.

Additional Notes

Excluded unrelated local changes from this PR scope:

• README.md
• apps/web-evals/next-env.d.ts
• packages/types/package.json
• turbo.json

Get in Touch

Discord: santy2509

Interactively review PR in Roo Code Cloud

[saneroen]