docs: migration analysis skill improvements

[rise-erpelding]

Description

Improves the migration-analysis-prompt.md used for generating component migration documentation. Changes address recurring issues identified during human review of AI-generated docs, including branch confusion, missing diffs, verbose summaries, and incorrect status classifications.

Motivation and context

• During review of generated migration docs (link, tag, taggroup, tooltip), several patterns of errors were identified:
  TagGroup incorrectly stated "no changes in Spectrum 2" due to branch verification failures
• Diff sections were often prose descriptions instead of actual unified diffs
• Summary sections included structure descriptions instead of focusing on changes
• Features removed in Spectrum 2 were marked "Missing from CSS" instead of "Deprecated"
• These changes make the prompt more explicit about requirements to reduce errors and improve output quality.

Related issue(s)

• Related to ongoing 2nd-gen component analysis work

• fixes [Issue Number]

Summary of changes

Commits are separated for easier review:

1. Branch verification protocol - Requires proof of correct branch (git output, quoted imports, distinguishing features)
2. Mandatory diff generation - Adds git diff command and makes diff section required
3. HTML diff format - Provides realistic example showing actual structural changes
4. Summary writing guidelines - Constrains summaries to change-focused bullets only
5. CSS selector categorization - Requires organizing selectors by type (base, variants, states, etc.)
6. Name equivalence mapping - Guides recognition of same concepts with different names
7. --mod change tracking - Notes --mod changes as signals for new/deprecated features
8. Deprecation detection criteria - Expands when to use "Deprecated" vs "Missing from CSS"
9. Documentation goal statement - Frames output for engineers estimating migration work
10. Quality gates checklist - Self-check before completion

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed at the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes.
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

---

Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are approved before the author can update Golden Hash

Manual review test cases

• Descriptive Test Statement

  1. Go here
  2. Do this action
  3. Expect this result

• Descriptive Test Statement

  1. Go here
  2. Do this action
  3. Expect this result

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

[changeset-bot]

⚠️ No Changeset found

Latest commit: 5f7224e

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

📚 Branch Preview Links

• Documentation Site (first-gen)
• Storybook (first-gen)
• Storybook (second-gen)

🔍 First Generation Visual Regression Test Results

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

Deployed to Azure Blob Storage: pr-5995

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.