v0.5.1 — initial public release

Fixed — version source-of-truth + INSTALL TODO

External review of the freshly-shipped v0.5.0 bundle surfaced three
real findings: the human-facing docs still claimed v0.1.x / v0.2.0,
the MCP server announced itself as 0.2.0 regardless of package
version, and INSTALL.md carried an unimplemented
pd init --regenerate-schemas command marked TODO: не реализована.
All three patched in one go.

• Docs versioned and machine-checked. README.md, OVERVIEW.md,
  and INSTALL.md now declare v0.5.1 on a line tagged with the
  <!-- pd:version --> marker. The version source-of-truth vitest
  scans those markers and asserts the embedded semver matches the
  CLI manifest — future drift breaks pnpm test instead of slipping
  to an external reviewer.
• MCP SERVER_VERSION follows package.json. Mirrors the
  pattern already used by CLI_VERSION: a tiny packages/mcp/src/version.ts
  loads the manifest via createRequire, the constant re-exports
  from there. No more hardcoded literal, no more drift on bump.
• pd schemas regen [<dir>] — new CLI command that refreshes
  <space>/schemas/*.json from the current Zod source. Drop-in
  replacement for the old "delete schemas/ and re-init in a temp
  dir" workaround documented in INSTALL.md. Useful after upgrading
  the pd binary on an existing space.

Notes

Plain pd validate spaces/pizza-shop-demo stays 0 errors / 0 warnings.
Tests: 355/355 plus three new version-source-of-truth assertions
(MCP parity + doc markers).