build: offline verification, samples, and MCP gateway records

[jithinraj]

Summary

Release preparation for v0.15.1: offline verification, generated samples, and MCP gateway records. Bumps all workspace package versions 0.15.0 -> 0.15.1 plus the version-bearing metadata and generated artifacts; adds the CHANGELOG entry. No wire, schema, signing, or registry changes; the public API change in this release line is additive (peac verify --public-key, merged in #833).

Scope

• pnpm version:bump 0.15.1 (65 packages; publish manifest; MCP server.json/manifest.json; spec and conformance version fields; build-registry constant).
• Manual version sites: mcp-server SERVER_VERSION, smithery.yaml pin, docs/releases/facts.json version and test metrics, package-surface-audit allowlist, telemetry version constant, regenerated kernel error tables and conformance matrix.
• CHANGELOG: new 0.15.1 section; the date convention keeps dates on the newest and earliest entries only.
• Mutable release-state fields (release_date, dist_tag) intentionally remain at pre-release values; they are stamped post-tag per docs/RELEASING.md.

Validation

• Full suite: 11,525 tests passed (459 files). Conformance: 676 passed (19 files); schema lint and fixture validation pass.
• verify-release: 0 failed (build_targets matches turbo dry-run: 105).
• guard, publish-list, manifest-topo, audit-exception --strict, version sync: all pass.
• Built-CLI smoke: peac --version reports 0.15.1; samples generate -> verify --public-key verifies offline; example demos pass.