Add EC2 Launch Template strain genesis for AWS horizontal scale.

Ship POST /api/v1/forge/launch-template with cloud-init user-data embedding genesis snapshot hash and strain card ID; first template-tagged auth pins SpreadGeneration=0 and ParentAgentID=template.

server/internal/builder/launch_template_handler.go

@@ -0,0 +1,24 @@
+package builder
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+func (h *Handler) ServeLaunchTemplate(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	var req LaunchTemplateRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeJSON(w, http.StatusBadRequest, LaunchTemplateResponse{Success: false, Error: "invalid JSON"})
+		return
+	}
+	resp, err := BuildLaunchTemplateArtifacts(req)
+	if err != nil {
+		writeJSON(w, http.StatusBadRequest, resp)
+		return
+	}
+	writeJSON(w, http.StatusOK, resp)
+}