feat: add native person primitive parity surfaces

[G9Pedro]

Summary

• promote person, client, and project into the retained native primitive model and separate retained/canonical semantics from built-in origin
• add native CLI primitive-type/primitive/person command surfaces on top of the shared kernel contract
• expand MCP primitive discovery/CRUD with native person affordances and parity tests

Testing

• pnpm run typecheck
• pnpm run build
• pnpm exec vitest run packages/kernel/src/registry.test.ts packages/kernel/src/bases.test.ts packages/kernel/src/workspace.test.ts packages/kernel/src/store.test.ts packages/mcp-server/src/mcp-server.test.ts packages/mcp-server/src/mcp-http-server.test.ts tests/cli-person-commands.test.ts packages/testkit/src/contracts/schema-conformance.test.ts

Notes

• includes an implementation plan document at docs/plans/2026-04-20-001-feat-native-person-primitive-plan.md
• the final shape keeps generic primitive type/instance CRUD as the canonical platform contract, with native person overlays in both CLI and MCP