chore: prepare wbot 0.2.0 stable release

[Deniffer001]

Publish stable 0.2.0 from 0.2.0-rc.1, synchronizing the package, lockfile, Codex and Claude plugin manifests, and pinned runtime artifact URLs. Add migration steps from 0.1.x; RC consumers have no additional API migration.

Remove a hardcoded current-version assertion from the release-impact test. Existing CLI, MCP, plugin, and artifact version-consistency tests remain in place.

Validation:

• Frozen dependency install, formatting/lint, typecheck, and all 47 tests passed locally.
• PR CI passed, including package installation verification.
• Candidate 0.2.0 artifact, release preflight, and curated release notes verified.
• Candidate 0.2.0 and checksum-verified published 0.1.2 artifacts each successfully read conversations, history, and updates from the current test Platform.
• Live candidate MCP dogfood passed: version handshake, three read-only tools, text/structured projection equality, capabilities/freshness, history and updates cursor continuation, invalid-cursor errors, and the HTTP unauthorized envelope.
• The required test credential is configured in Actions Secrets.

The published-client/backend check was performed manually against the current test deployment. Automating that check in backend deployment CI remains a separate follow-up; no backend is deployed by this PR.

Merging this version change into main triggers the public stable release. The release workflow reruns its candidate-artifact compatibility gate before creating the immutable tag and assets.