docs: consolidate all documentation under docs/ and enforce single-source rule
Migrate all docs scattered across hidden folders into docs/:
- .compozy/tasks/ → docs/planning/ (PRDs, tech specs, tasks, memory) and docs/adr/ (ADRs by phase)
- .specs/ → docs/specs/ (codebase, features, project specs)
- .docs/ → docs/legacy/ (legacy reference implementation docs)
- .discussions/ → docs/discussions/ (design discussions and open questions)
Delete .compozy/, .specs/, .docs/, and .discussions/.
Update AGENTS.md: add explicit docs/ location table, hard rule against hidden doc folders,
and new AI-assisted development section (context lazy loading, scope control, verification).
Update CLAUDE.md: fix .docs/ references to docs/legacy/.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
