feat: Variantenmanagement — Sub-Projekte mit GAP-Analyse

Backend:
- parent_project_id auf iace_projects (DB + Go Struct)
- POST/GET /variants + GET /variant-gap Endpoints
- GAP-Analyse: Differenz Hazards/Massnahmen/Kategorien

Frontend:
- VariantPanel auf Projekt-Uebersicht
- Variante erstellen Dialog
- Sidebar-Anzeige (Variantenanzahl / Basis-Link)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -308,3 +308,88 @@ func (h *IACEHandler) InitFromProfile(c *gin.Context) {
 		"regulations_triggered": triggeredRegulations,
 	})
 }
+
+// ============================================================================
+// Variant Management
+// ============================================================================
+
+// CreateVariant handles POST /projects/:id/variants
+// Creates a new variant sub-project linked to the given base project.
+func (h *IACEHandler) CreateVariant(c *gin.Context) {
+	parentID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid project ID"})
+		return
+	}
+
+	// Verify parent project exists
+	parent, err := h.store.GetProject(c.Request.Context(), parentID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	if parent == nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "parent project not found"})
+		return
+	}
+
+	var req iace.CreateProjectRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	// Force the parent link
+	req.ParentProjectID = &parentID
+
+	project, err := h.store.CreateProject(c.Request.Context(), parent.TenantID, req)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusCreated, gin.H{"project": project})
+}
+
+// ListVariants handles GET /projects/:id/variants
+// Returns all variant sub-projects for a given base project.
+func (h *IACEHandler) ListVariants(c *gin.Context) {
+	parentID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid project ID"})
+		return
+	}
+
+	variants, err := h.store.ListVariants(c.Request.Context(), parentID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	if variants == nil {
+		variants = []iace.Project{}
+	}
+
+	c.JSON(http.StatusOK, iace.ProjectListResponse{
+		Projects: variants,
+		Total:    len(variants),
+	})
+}
+
+// GetVariantGap handles GET /projects/:id/variant-gap
+// Returns a gap analysis comparing a variant against its base project.
+func (h *IACEHandler) GetVariantGap(c *gin.Context) {
+	variantID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid project ID"})
+		return
+	}
+
+	gap, err := h.store.GetVariantGap(c.Request.Context(), variantID)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gap)
+}