feat(iace): project-wide risk matrix (Severity × Probability)

Adds GET /projects/:id/risk-matrix — a confidence-aware risk view computed
on read from each hazard's category/scenario/lifecycle using the SAME model
as the GT benchmark (no persistence, so it never goes stale against the
model; the hand-defaulted iace_hazards risk columns stay untouched).

- risk_matrix.go: EstimateHazardRisk (single source of truth for S/F/W/P +
  range + level + confidence) and BuildRiskMatrix (per-hazard list + a 5×5
  Severity×Probability aggregation grid with dominant level per cell).
- Frontend: RiskMatrix grid in the Risikobewertung tab (muted colours per
  the confidence-aware tonality), level counts + tool-confidence summary,
  fed by useRiskMatrix. Shows risk for EVERY project, not only GT ones.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ai-compliance-sdk/internal/app/routes_iace.go

@@ -71,6 +71,7 @@ func registerIACERoutes(v1 *gin.RouterGroup, h *handlers.IACEHandler) {
 		iaceRoutes.POST("/projects/:id/hazards/:hid/assess", h.AssessRisk)
 		iaceRoutes.GET("/projects/:id/hazards/:hid/risk-suggestion", h.GetRiskSuggestion)
 		iaceRoutes.GET("/projects/:id/risk-summary", h.GetRiskSummary)
+		iaceRoutes.GET("/projects/:id/risk-matrix", h.GetRiskMatrix)
 		iaceRoutes.GET("/projects/:id/suggested-norms", h.SuggestProjectNorms)
 		iaceRoutes.POST("/projects/:id/hazards/:hid/reassess", h.ReassessRisk)