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>

tools/diagram_spec_validator.py

@@ -29,6 +29,23 @@ Returns a dict with:
   - issues: [{"severity", "code", "message", "id"}]
 
 Severity ``error`` → renderers raise. ``warn`` → printed to stderr.
+
+Policy on legacy archcenter reproductions
+-----------------------------------------
+Specs under ``examples/eval-*-archcenter-native-*/`` are auto-generated
+reconstructions of Oracle Architecture Center references. Oracle's own
+geometry sometimes places labels 2-5px from container edges, and the
+reproductions mirror those coordinates verbatim to keep the perceptual
+diff against the canonical PNGs above the fidelity threshold. Touching
+them to silence ``LABEL_NEAR_PARENT_EDGE`` (severity=warn) would risk
+the pixel-fidelity scores tracked by ``archcenter_batch_driver``.
+
+The validator therefore distinguishes:
+
+  - ``LABEL_OVERFLOW_PARENT`` (error, blocks render): label bottom is
+    OUTSIDE the parent — true regression.
+  - ``LABEL_NEAR_PARENT_EDGE`` (warn, never blocks): label sits within
+    6px but still inside — common in Oracle's own ref archs.
 """
 from __future__ import annotations