[#625] Removed unmaintained 2.x to 3.x migration information.

[AlexSkrypnyk]

Closes #625

Summary

Removed the unmaintained 2.x to 3.x migration information from the project. The migration guide and the AI-guided migration prompt were no longer kept up to date and added noise to the README and the repository root. With 3.x being the stable line for some time, this legacy material is no longer necessary.

Changes

• README.md: Removed the [!TIP] block that pointed users to the migration map and the <details> block containing the AI-guided migration prompt.
• MIGRATION.md: Deleted the migration map file that documented the 2.x to 3.x step renames.
• .gitattributes: Removed the MIGRATION.md entry from the export-ignore list.
• CLAUDE.md: Removed the bullet referencing MIGRATION.md from the Documentation section.

Before / After

Before                          After
------                          -----
README.md                       README.md
  [!TIP] migration block          (removed)
  <details> AI prompt             (removed)
MIGRATION.md                    (deleted)
.gitattributes                  .gitattributes
  /MIGRATION.md export-ignore     (removed)
CLAUDE.md                       CLAUDE.md
  - Migration guide: MIGRATION    (removed)

Summary

This PR removes legacy v2→v3 migration materials that are no longer maintained or useful, now that version 3.x is stable.

Changes

Files Deleted

• MIGRATION.md (214 lines): Comprehensive migration map documenting v2→v3 step definition trait renames and transformations (e.g., BlockTrait → Drupal\BlockTrait, ContentBlockTrait → Drupal\ContentBlockTrait), removed steps, and restructured step phrasing/parameters.

Files Modified

• README.md (−177 lines): Removed the "[!TIP] Upgrading from 2.x?" section containing a collapsible <details> block with AI-generated migration prompt, package update steps, namespace import examples, and migration troubleshooting guidance.
• CLAUDE.md (−1 line): Removed the documentation link entry "Migration guide for upgrading from 2.x: MIGRATION.md" from the Documentation section.
• .gitattributes (−1 line): Removed the MIGRATION.md entry marked with export-ignore, so this file would no longer be excluded from distribution archives (note: file is now deleted anyway).

Assessment

No violations of the step definition rules defined in CONTRIBUTING.md were introduced or removed by these changes. The PR removes documentation materials rather than modifying step definitions themselves. The step definition format and naming convention guidelines remain intact and applicable to all current step definitions in the codebase.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: e996e992-18f8-491e-9015-592a762fd035

📥 Commits

Reviewing files that changed from the base of the PR and between 320fd09 and db3fcb4.

📒 Files selected for processing (4)

• .gitattributes
• CLAUDE.md
• MIGRATION.md
• README.md

💤 Files with no reviewable changes (4)

• .gitattributes
• CLAUDE.md
• README.md
• MIGRATION.md

---

Walkthrough

This PR removes v2-to-v3 migration documentation from the repository, including the deletion of MIGRATION.md and removal of all upgrade guidance references from README.md, CLAUDE.md, and .gitattributes. The changes reflect a full deprecation of v2 migration support as v3 is now the established version.

Changes

Cohort / File(s)	Summary
Migration documentation removal MIGRATION.md	Entire file deleted containing v2→v3 migration mappings for step definition traits, step text translations, and assertion updates (214 lines removed).
Migration references removal .gitattributes, CLAUDE.md, README.md	Removed all pointers to migration documentation: deleted MIGRATION.md from export-ignore in .gitattributes, removed migration guide link from CLAUDE.md, and eliminated the collapsible "Upgrading from 2.x?" section with embedded migration instructions from README.md.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• [#368] Updated BlockContentTrait. #374: Modifies MIGRATION.md mappings directly; contrasts with this PR's complete removal of the file.
• Updated docs. #395: Adds MIGRATION.md to export-ignore and documentation references; opposes this PR's deletion and reference removal.
• Expose STEPS.md file to consumer projects. #397: Modifies .gitattributes and CLAUDE.md documentation visibility; affects the same files being changed here.

Suggested labels

PR: Requires more work

Poem

🐰 The old paths fade as v3 takes the lead,
Migration maps no longer what we need,
Hop forward, friends, to brighter days ahead,
The v2 guide now rests where old things are fed! 🌿

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically summarizes the main change: removing unmaintained 2.x to 3.x migration information across multiple files.
Linked Issues check	✅ Passed	The pull request fully addresses the objectives in issue #625 by removing all outdated migration information from README.md, MIGRATION.md, .gitattributes, and CLAUDE.md.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to removing migration-related content as required by issue #625; no unrelated modifications are present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/625-remove-migration

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.45%. Comparing base (320fd09) to head (db3fcb4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #627   +/-   ##
=======================================
  Coverage   97.45%   97.45%           
=======================================
  Files          44       44           
  Lines        3024     3024           
=======================================
  Hits         2947     2947           
  Misses         77       77           

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