Prepare v0.5.1 release

[samtay32]

What changed

• bump npm package, lockfile root, Codex plugin manifest, and CLI fallback to 0.5.1
• move the greenfield doctor fix from Unreleased into the dated 0.5.1 changelog section
• document the compatible patch upgrade impact and additive doctor reason codes

Why

PR #13 fixed misleading human guidance for newly initialized empty projects while retaining fail-closed validation. This patch prepares that reviewed behavior for a synchronized npm and GitHub release.

Validation

• npm run release:check passed: 65/65 tests, package dry-run, and packed-install smoke
• package dry-run contains exactly 77 intended files as ultimate-agent-stack@0.5.1
• all 48 tracked Markdown files passed markdownlint-cli2@0.18.1
• package, lockfile, plugin manifest, and CLI fallback all report 0.5.1
• npm registry and Git tag preflight confirm 0.5.1 is unused
• git diff --check passed

Release boundary

This PR prepares source metadata only. It does not publish npm or create a GitHub Release.

Summary by CodeRabbit

• Release
  • Updated the product version to 0.5.1.
  • Added release notes documenting compatibility and additive diagnostic reason codes.
  • Preserved existing fail-closed behavior and Git, validation, and approval requirements.

[samtay32]

@coderabbitai review

[coderabbitai]

📝 Walkthrough

Walkthrough

The patch updates package and plugin version metadata from 0.5.0 to 0.5.1, aligns the fallback package version, and adds the 0.5.1 changelog release notes.

Changes

0.5.1 release metadata

Layer / File(s)	Summary
Version synchronization and release notes .codex-plugin/plugin.json, package.json, bin/ultimate-agent-stack.mjs, CHANGELOG.md	Package, plugin, and fallback version values are updated to 0.5.1, with corresponding release and upgrade-impact notes added to the changelog.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related PRs

• samtay32/ultimate-agent-stack#5: Updates the same package, plugin, and fallback version sources.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: preparing the v0.5.1 release.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/release-v0.5.1

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[coderabbitai]

✅ Action performed

Review finished.

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[samtay32]

@coderabbitai review

[coderabbitai]

✅ Action performed

Review finished.

Note: CodeRabbit is an incremental review system and does not re-review already reviewed commits. This command is applicable only when automatic reviews are paused.