feat(peer): add strict structured output and Brave evidence

[CBEPX]

Summary

• add strict Draft-07 output schemas for design, research, and critique Claude turns
• fail closed before Claude spawn when a peer schema is unavailable
• accept exactly the audited Brave web search and LLM-context tool IDs
• require exact Brave evidence to be present in the frozen selected-tool manifest
• document provider drift/disclosure boundaries and prepare version 1.7.2
• isolate the missing-schema regression without mutating tracked files

Verification

• Claude Opus exact-head review: approve with nits; no correctness defects
• independent strong review: READY, no P0-P3 findings
• npm run check: 931 unit, 104 integration, 24 E2E
• coverage: 1,059/1,059; 92.63% statements/lines, 83.51% branches, 98.27% functions
• forced mutation: critical 82.65%, managed 74.69%, installer 66.39%
• npm pack --dry-run: 92 files, including all three peer schemas
• design/research skill entrypoints validated

Follow-ups

• Preserve bounded diagnostics for peer output schema load failures #25
• Make the annotationless MCP audit registry immutable #26
• Add an opt-in live Claude and Brave peer qualification gate #27