fix: resolve build errors in serial command handlers

- Add const qualifier to CommandEntry::commandHandler()
- Explicit std::string conversion in hostname handleSet
- Use push_back instead of append for single char in validgpios

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

Author: hhvrc

include/serial/command_handlers/CommandEntry.h

@@ -15,7 +15,7 @@ namespace OpenShock::Serial {
     inline std::string_view name() const { return m_name; }
     inline std::string_view description() const { return m_description; }
     inline const std::vector<CommandArgument>& arguments() const { return m_arguments; }
-    inline CommandHandler commandHandler() { return m_commandHandler; }
+    inline CommandHandler commandHandler() const { return m_commandHandler; }
 
     CommandArgument& addArgument(std::string_view name, std::string_view constraint, std::string_view exampleValue, std::vector<std::string_view> constraintExtensions = {});
 

src/serial/command_handlers/hostname.cpp

@@ -27,7 +27,7 @@ static void handleGet(std::string_view arg, bool isAutomated)
 
 static void handleSet(std::string_view arg, bool isAutomated)
 {
-  bool result = OpenShock::Config::SetWiFiHostname(arg);
+  bool result = OpenShock::Config::SetWiFiHostname(std::string(arg));
   if (result) {
     SERPR_SUCCESS("Saved config, restarting...");
     esp_restart();

src/serial/command_handlers/validgpios.cpp

@@ -20,7 +20,7 @@ static void handleValidGpios(std::string_view arg, bool isAutomated)
   for (std::size_t i = 0; i < pins.size(); i++) {
     if (pins[i]) {
       buffer.append(std::to_string(i));
-      buffer.append(',');
+      buffer.push_back(',');
     }
   }