v1.37.0 — lean MCP payloads, semantic that can't dead-end, MCP↔CLI parity

1.37.0 — lean MCP payloads, semantic that can't dead-end, MCP↔CLI parity

Driven by the third field report (v1.36 head-to-head vs ripgrep on a 5-project
monorepo — structural queries won; three defects found, all fixed).

• MCP routes was unusable by its own client (232 KB single-line JSON,
  rejected by Claude Code): each route serialized the FULL graph node.
  Now: lean rows ({method, path, handler, file, line}) + limit/offset
  pagination + path_prefix/method filters; 560 routes ≈ 6 KB. Same lean
  sweep applied to every list-shaped MCP response that still leaked full
  nodes: implementers, dead_code, pinned callers. One shared lean
  serializer; full node detail stays behind get_node(id).
• semantic_search can no longer dead-end: with no embedder it degrades
  to lexical search and says so ("degraded": "lexical fallback — no embedder…") instead of hard-failing a tool it advertised. stats reports
  embedder_available up front so agents route around it. install.sh now
  builds with local-embed (bundled bge-small) by default — and
  indexstore on macOS — so the stock install answers semantic queries out
  of the box. CODEGRAPH_NO_EMBEDDER=1 forces lexical-only (also the
  deterministic test hook).
• MCP↔CLI naming parity: semantic-search/semantic_search →
  semantic, blast-radius/blast_radius → impact,
  trace-path/trace_path → trace, graph-query/graph_query →
  cypher, dead_code → dead-code (joins the earlier stats → status).
  Agents translate MCP names to CLI constantly; every advertised name now
  resolves.
• Regression tests: routes payload cap (<25 KB on 300 routes) + pagination +
  filters, alias resolution for every MCP name, forced no-embedder
  degradation with embedder_available:false in stats.