docs: add 0.2.0 changelog for lock-order and parity work

[clean6378-max-it]

Closes #141
Docs-only. Adds a [0.2.0] section to CHANGELOG.md for the Week 30 work in #138, #139, and #140: the search-index lock-order doc, the concurrency suite, and the Python/JS parity oracles. Clears [Unreleased] and updates the footer compare links. No version bump here; that lands in the release PR.

git diff --stat should show only CHANGELOG.md.

Summary by CodeRabbit

• Documentation
  • Added release notes for version 0.2.0.
  • Documented search-index locking/threading and forbidden nesting rules.
• New Features
  • Added schema-report API with user-facing messaging when upstream JSONL fields change.
  • Improved search with FTS5 index-first behavior and background rebuilds.
• Changed
  • Improved tool-type syncing at SPA startup and added drift warnings.
  • Consolidated session/stats/export handling and aligned export error codes with the HTTP API.
• Bug Fixes / Improvements
  • Improved error handling (including locked-index/live-scan behavior) and fixed YAML frontmatter quoting.
  • Added/expanded concurrent search and Python/JavaScript parity tests.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 3ddc2815-ff30-443d-80a0-ad9de9d6190d

📥 Commits

Reviewing files that changed from the base of the PR and between e87f05e and dc66af3.

📒 Files selected for processing (1)

• CHANGELOG.md

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📝 Walkthrough

Walkthrough

The changelog adds a dated 0.2.0 release section describing documentation, testing, search, caching, API, and export changes, and updates the Unreleased and 0.2.0 comparison links.

Changes

Release documentation

Layer / File(s)	Summary
Add 0.2.0 release details CHANGELOG.md	Adds the 0.2.0 release notes and updates the version comparison references.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Suggested reviewers: timon0305

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The changelog also includes unrelated Week 30 items like tool registry, schema report, caches, search, and API refactors.	Trim the section to the lock-order doc, concurrency tests, parity oracle entries, and footer updates only.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately reflects the changelog update for lock-order and parity work.
Linked Issues check	✅ Passed	It adds the required 0.2.0 section, references the requested files, clears Unreleased, and updates compare links.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/changelog-0-2-0

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_{Comment @coderabbitai help to get the list of available commands.}

[wpak-ai]

document the user-facing changes shipped since v0.1.0 in the [0.2.0] section, not only the three internal PRs #138–#140 (eleven user-visible changes, #104, #105, #107, #108, #111, #120, #121, #122, #125, #127, #134, merged after v0.1.0 and were never recorded in [Unreleased] or [0.1.0], so tagging v0.2.0 with only three internal items leaves them with no release section to belong to and omits them from the Release notes that is-12 copies out of this section)

[clean6378-max-it]

document the user-facing changes shipped since v0.1.0 in the [0.2.0] section, not only the three internal PRs #138–#140 (eleven user-visible changes, #104, #105, #107, #108, #111, #120, #121, #122, #125, #127, #134, merged after v0.1.0 and were never recorded in [Unreleased] or [0.1.0], so tagging v0.2.0 with only three internal items leaves them with no release section to belong to and omits them from the Release notes that is-12 copies out of this section)

Expanded [0.2.0] to cover all eleven user-facing PRs since v0.1.0