chore(release): 4.1.0

[kkdev92]

Release 4.1.0 — a minor. The full text is the 4.1.0 entry in CHANGELOG.md.

Everything is additive; the API 4.0.1 exposed is unchanged and the VS Code floor stays at ^1.134.0.

• describePlan turns a compiled plan into JSON; PreflightError.problems reports a preflight failure as data; a shutdown timeout names what was holding it, and createTestHost().inspect() answers what leaks() cannot (feat(diagnostics): say what a shutdown that ran out of budget was still holding #45, feat(plan): describe a compiled plan as JSON #46, feat(preflight): report each problem as data, with a stable code #47).
• A command-line tool, vscode-ext-kit plan and vscode-ext-kit manifest: the plan as JSON or a graph, preflight as an exit code, and the manifest comparison — with --apply for the mechanical part (feat(cli): print, draw and check the plan an extension compiles #49, CLI: manifest command; defineSettings({ contributed: false }) for sections an extension only reads #52).
• diffManifest returns what assertManifestMatches used to only throw; defineSettings({ contributed: false }) declares a section the extension only reads (feat(testing): return manifest disagreements as data #50, CLI: manifest command; defineSettings({ contributed: false }) for sections an extension only reads #52).
• An API reference generated from the JSDoc, with the types public signatures name now exported (Generate the API reference; export the types public signatures name #51), and a step-by-step migration guide from 2.x (Docs: a step-by-step migration guide from 2.x #53, Docs: the migration guide's manifest step names the command line and contributed: false #54).
• The one behaviour change: defineExtension is single-use — a second activate after deactivate rejects instead of building a second application. Visible only to a test that activated one result twice (feat(extension): make defineExtension single-use, like the host it serves #48).

This PR bumps the version, dates the changelog entry, and updates the README status line and the supported-versions table. Tagging v4.1.0 after the merge runs the release workflow.

🤖 Generated with Claude Code