feat: add source-backed architecture context

[Helweg]

Summary

• add portable architecture_context repository maps across OpenCode, MCP, and Pi
• ground module responsibilities, boundaries, hubs, recent activity, and graph uncertainty in source evidence
• add architecture evaluation datasets, token-cost budgets, and end-to-end host contract coverage

Validation

• npm run test:run (104 files, 1619 tests)
• npm run build:ts
• npm run typecheck
• npm run lint

Closes #319