feat: add highway synthesis proposals

[bntvllnt]

Summary

• Add highways --propose synthesis opportunities when repeated operation/shape/sink routes have no canonical node.
• Return proposed highway name, file, signature, skeleton, reroute plan, cycle-safety evidence, and context-pack next command through CLI and MCP.
• Sync README, docs, llms files, and 2.5.0 roadmap shipped status for CH-P2-02.

Verification

• pnpm lint
• pnpm typecheck
• pnpm vitest run tests/highways.e2e.test.ts tests/operation-registry.e2e.test.ts tests/operation-registry.test.ts tests/mcp-tools.test.ts --reporter=verbose --pool threads --no-file-parallelism --maxWorkers=1
• pnpm test -> 33 files / 466 tests
• pnpm verify:cli-real -> 62/62
• git diff --check
• Built CLI dogfood: generated synthesis fixture emits createUserDraft, safe cycle check, and 3 affected routes.

Review

• $code-review Production mode completed after fix loop.
• Local artifact: /tmp/code-review-highways-h2.json
• Coverage: 36/36 hunks, 13/13 relevant rules, final verdict CLEAN.

Release

• Stable release intentionally not cut.
• Canary verification will run after merge via Publish workflow.