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

cmd/server/main.go

@@ -45,6 +45,7 @@ func main() {
 		protectedRoutes.Use(authMgr.Middleware)
 		protectedRoutes.Get("/", uiHandler.Dashboard)
 		protectedRoutes.Get("/agents/{id}", uiHandler.AgentDetail)
+		protectedRoutes.Post("/agents/{id}/hostname", uiHandler.UpdateAgentHostname)
 		protectedRoutes.Post("/logout", uiHandler.Logout)
 		protectedRoutes.Post("/api/agents/remove-stale", uiHandler.RemoveStaleAgents)
 		protectedRoutes.Post("/api/agents/{id}/delete", uiHandler.DeleteAgent)