Diagram tooling: make targets, CI gate, LLM-rewrite hook, refresh docs

Implements points 3–8 of the post-procedure follow-up.

- Make targets: diagram-lookup, diagram-validate-spec, diagram-spec-audit,
  archcenter-descriptions-refresh, archcenter-smoke. Promotes the new
  tools out of "remember the CLI" into discoverable build-automation.
- .gitea/workflows/diagram-validators.yaml — runs spec validator across
  every absolute_layout spec on push/PR, plus a drawio re-render smoke
  test on the canonical example. Hard fail blocks merges.
- archcenter_pattern_lookup --llm-rewrite — opt-in (ANTHROPIC_API_KEY
  env var, mirroring DRAWIO_EXE pattern). Rewrites natural-language
  queries into canonical OCI terminology before scoring; falls back to
  the original query on any error.
- diagram_spec_validator — documents the policy on legacy archcenter
  reproductions: LABEL_NEAR_PARENT_EDGE stays a warning so verbatim
  reconstructions don't lose pixel-fidelity from cosmetic edits.
- README — documents the asset refresh procedure (downloader +
  description fetcher are idempotent, refresh quarterly).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -178,8 +178,13 @@ python tools/archcenter_pattern_lookup.py "fastconnect exacs cross region" --top
 
 # Re-fetch description text after a catalog refresh
 python tools/archcenter_description_fetcher.py --limit 200
+
+# Re-download cached drawio/svg/png assets after a catalog refresh
+python tools/archcenter_zip_downloader.py    # idempotent; skips slugs whose folder already has a .drawio
 ```
 
+The cached assets under `kb/diagram/assets/archcenter-refs/` (~83MB) are committed so the skill works offline. Refresh quarterly or when `refresh_arch_catalog.py --whats-new` adds entries — both downloader and description fetcher are idempotent and only fetch what's missing.
+
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