feat(iace): wire OSHA minimum-distance library into measures + endpoint

The May-built OSHA distance library (minimum_distances.go, 29 CFR 1910,
US public domain) was dead code — zero callers, no route, no test, while
the mm values that actually appear in measures are independent hand-prose
(some carrying ISO 13854/13857 values, not OSHA).

This surfaces it without touching the measures response contract:
- GET /iace/minimum-distances (+ ?measure_id=) returns the distances, the
  curated measure→distance link table and the licensing note.
- AllMeasureDistanceLinks/MinimumDistancesForMeasure resolve only the
  defensible links (M600 value_source; M254/M065 public-domain crossref to
  ISO), with the relation made explicit so the join stays honest.
- architecture.go lists the OSHA library so it shows in the audit explainer.
- Tests: inch→mm conversion + license completeness, link integrity, and a
  consistency test pinning that a value_source measure's prose still
  matches the OSHA source (codifies the audit finding as a regression gate).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ai-compliance-sdk/internal/api/handlers/iace_handler_distances.go

@@ -0,0 +1,30 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/breakpilot/ai-compliance-sdk/internal/iace"
+	"github.com/gin-gonic/gin"
+)
+
+// ListMinimumDistances handles GET /minimum-distances.
+// Read-only OSHA safety-distance reference (29 CFR 1910, US public domain)
+// plus the curated measure→distance link table, so an auditor can see WHERE a
+// measure's mm figure comes from. Optional ?measure_id= returns only the
+// distances (and links) tied to that protective measure.
+func (h *IACEHandler) ListMinimumDistances(c *gin.Context) {
+	if mid := c.Query("measure_id"); mid != "" {
+		c.JSON(http.StatusOK, gin.H{
+			"measure_id": mid,
+			"distances":  iace.MinimumDistancesForMeasure(mid),
+			"links":      iace.LinksForMeasure(mid),
+			"note":       iace.MinimumDistanceNote,
+		})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"distances": iace.GetOSHAMinimumDistances(),
+		"links":     iace.AllMeasureDistanceLinks(),
+		"note":      iace.MinimumDistanceNote,
+	})
+}