ci(release): adopt changesets for versioning and release notes

[Salmatcre8]

Summary

Adopts changesets so Lens gets semver-tracked changelogs, PR-based version bumps, and a one-button release workflow instead of manual releases.

Closes #58

What was added

• .changeset/config.json — changesets configuration (baseBranch: main, access: restricted, default changelog generator).
• .github/workflows/release.yml — uses the official changesets/action on push to main. When changesets are pending it opens/updates a "Version Packages" PR; when that PR is merged it bumps the version, creates a git tag, and a GitHub release.
• package.json — adds @changesets/cli (devDependency) and scripts:
  • changeset — add a changeset
  • version-packages — changeset version (used by the Version PR)
  • release — changeset tag (used on merge)
• CONTRIBUTING.md — new Releases section explaining how to add a changeset and how the release flow works.
• .changeset/initial-changesets-adoption.md — an initial patch changeset so the first push to main opens a Version PR.

Not publishing to npm

Lens is not published to a registry, so there is no npm publish step — the release step runs changeset tag, which only creates git tags (matching the issue's "just tag" requirement).

Validation

• npx changeset status → detects lens@0.1.1 (patch) from the initial changeset (config + changeset valid).
• npx tsc --noEmit → passes (no source changes).

Acceptance criteria

• Running npx changeset creates a markdown file
• Pushing to main with pending changesets opens a Version PR (via changesets/action)
• Merging the Version PR bumps version and tags
• CONTRIBUTING explains the workflow

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