Show readiness score feedback in a drawer

What does this MR do and why?

Opens readiness feedback in a 400px overlay drawer, so users can read the assessment without resizing the work item page.

• Score details toggles the drawer from the readiness indicator.
• Shows an introduction, sanitized Markdown feedback, and an information box with a Learn more link.
• Keeps the readiness level in the widget; the drawer focuses on feedback.
• Shows the indicator only once a numeric score exists, including zero.
• Fetches feedback only while the drawer is open and workplan_score is enabled.
• Uses local drawer state, with Escape and focus restoration. Opening and closing leave the URL unchanged.
• Preserves the workplan panel and cached feedback through workplan edits.

Targets master; the earlier icon-placement and naming MRs are merged. Rescoring remains a follow-up.

References

• Resolves #628677
• Epic: gitlab-org#23050
• Design clarification: #628677 (comment 3944795102)
• Backend read path: !252884 (merged)
• Pending scoring state follow-up: #633076

Screenshots or screen recordings

Before: readiness popover	After: feedback drawer

How to set up and validate locally

1. Enable workplan_score for your current user in a project with planning enabled:

   Feature.enable(:workplan_score, User.find_by_username('root'))

2. Open a work item with a saved readiness score and feedback.
3. Select Score details. Verify the drawer overlays the page and shows formatted feedback and the information box.
4. Press Escape or Close drawer. Verify focus returns to Score details.
5. For a scored item without feedback, verify the No feedback available yet message.
6. Open the workplan panel, then readiness details. Verify closing the drawer leaves the workplan available.
7. Save a workplan and reopen readiness details. Verify feedback is retained without an extra query.

MR acceptance checklist

• Passed: 389 component tests across 14 suites; 30 cache tests after the rebase.
• Passed: targeted ESLint and formatting checks.
• Integration: local runs are blocked before tests execute by a missing generated fixture, graphql/commits/integration/get_commit_list_multiple_days.query.graphql.json. CI will validate these suites.
• Browser: verified the updated drawer on GDK work item 95. Screenshots above show the latest layout.
• Feature flag: default-off workplan_score; no changelog required.

Evaluate against the MR acceptance checklist.