feat: updated schema dialect metadata contract, schema composition, and docs

[mindsocket]

Summary

• implement schema dialect V2 metadata contract with top-level ``
• migrate hierarchy to .hierarchy.levels and remove legacy ._metadata behavior
• migrate rules to flat rules[] with per-rule category
• add deterministic metadata composition across `` graph (DFS + root last)
• enforce single hierarchy provider, aliases merge, and rules merge with explicit override: true
• add `` rule import support (specific rules and rule sets)
• update generated metaschema from in-code contract source
• update docs and agent references for final V2 structure, composition semantics, editor expectations, and migration guidance

Testing

• bun run lint
• bun run test
• bun run test:smoke (known failures in local configured spaces due timeouts/content-level best-practice violations)

Notes

• breaking changes are intentional per issue direction (no backward compatibility with legacy metadata structure)

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.