Add hostname editing feature to agent detail page

- Create enhanced agent detail template with all stats and hostname edit form
- Add UpdateHostname method to store for agent hostname updates
- Add UpdateAgentHostname handler in UI for web form submissions
- Add UpdateHostname endpoint in API handler for JSON requests
- Register new POST /agents/{id}/hostname route for hostname updates
- Improve agent detail page layout with Settings and Danger Zone sections
- Add error handling for missing agents and empty hostname values

internal/api/api.go

@@ -73,3 +73,32 @@ func (h *Handler) DeleteAgent(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
 	json.NewEncoder(w).Encode(map[string]string{"status": "deleted"})
 }
+
+// UpdateHostname updates the hostname for an agent.
+func (h *Handler) UpdateHostname(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	agentID := r.PathValue("id")
+	if agentID == "" {
+		http.Error(w, "missing agent id", http.StatusBadRequest)
+		return
+	}
+
+	hostname := r.FormValue("hostname")
+	if hostname == "" {
+		http.Error(w, "missing hostname", http.StatusBadRequest)
+		return
+	}
+
+	err := h.store.UpdateHostname(agentID, hostname)
+	if err != nil {
+		http.Error(w, "agent not found", http.StatusNotFound)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(map[string]string{"status": "updated"})
+}