refactor!: remove unfinished LazyBrain surfaces

[papperrollinggery]

Summary

Slim the current LazyBrain branch to the verified core surface:

• keep route, MCP, compile, embeddings, ready, statusline/status, diagnostics, and route event readback
• remove unfinished choices, adoption/regression, public jobs, repairs, doctor-fix, config-test/schema, Cytoscape UI, and long planning docs
• replace the oversized UI with a compact Workbench that only calls closed-loop APIs
• align README, README_CN, CHANGELOG, and CODEX_HANDOFF with actual shipped behavior

Verification

• npm run lint
• npm test: 725 passed
• npm run build
• npm run audit:public
• node dist/bin/lazybrain.js ready --release
• node dist/bin/lazybrain.js mcp status
• node dist/bin/lazybrain.js embeddings status
• node dist/bin/lazybrain.js route dogfood --target claude: PASS 40/40
• GitNexus detect_changes(scope=all): 14 indexed files, 27 symbols, 36 affected processes; risk remains critical because buildRouteSpec/route core paths are touched

Note

Plain ready can report NOT_READY on this machine when host load is above the hook fail-closed threshold. Release readiness passes because host load is intentionally ignored there.