feat!: rewrite SpecBridge as an AI system design and spec compiler

[HelloThisWorld]

Summary

• replace the legacy workflow and execution runtime with a clean-break SpecBridge 2.0 architecture
• add repository-grounded design sessions, authority and research gates, schema-first artifacts, a compiler, and structured review findings
• expose the exact 11-tool MCP surface plus a simplified CLI
• rebuild the Claude Code and Codex integrations as five thin 2.0 skills each
• replace legacy documentation and tests with migration guidance, golden scenarios, and end-to-end qualification

Breaking change

Legacy Job, Mission, WorkUnit, Attempt, runner, autonomy, template, extension, approval, build, and verification runtime contracts are removed. This PR intentionally does not provide compatibility shims or migrate legacy runtime state.

Validation

• pnpm lint
• pnpm typecheck
• pnpm test (24 tests)
• pnpm qualification (3 qualification tests)
• pnpm build
• pnpm smoke
• git diff --check