Code review fixes for M5Stack Unit C6L

- Fix strdup memory leak in repeater UITask: use stack buffer instead
- Remove redundant _display null check in companion UITask (already
  guarded at top of loop())
- Remove redundant build_src_filter exclusions in companion, repeater,
  and room_server envs (base config already handles them)
- Remove repeater UITask.h copy: include original header directly via
  relative path instead of maintaining a duplicate
- Remove unused -I flag for repeater subdirectory
- Delete upstream UnitC6LBoard.h/cpp (replaced by M5StackUnitC6LBoard)

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

Author: TheRealHaoLiu

variants/m5stack_unit_c6l/UnitC6LBoard.cpp

@@ -109,7 +109,7 @@ void UITask::loop() {
 
   if (_display->isOn()) {
     // Update marquee scroll
-    if (_display != NULL && _node_prefs != NULL && millis() >= _scroll_next) {
+    if (_node_prefs != NULL && millis() >= _scroll_next) {
       int nameW = _display->getTextWidth(_node_prefs->node_name);
       int w = _display->width();
       int maxScroll = nameW - w;

variants/m5stack_unit_c6l/UnitC6LBoard.h

@@ -67,7 +67,6 @@ build_flags =
 ;  -D MESH_PACKET_LOGGING=1
 ;  -D MESH_DEBUG=1
 build_src_filter = ${m5stack_unit_c6l.build_src_filter}
-  -<../variants/m5stack_unit_c6l/repeater/*.cpp>
   +<helpers/esp32/*.cpp>
   -<helpers/esp32/ESPNOWRadio.cpp>
   +<helpers/ui/SSD1306SPIDisplay.cpp>
@@ -82,7 +81,6 @@ lib_deps =
 [env:m5stack_unit_c6l_repeater]
 extends = m5stack_unit_c6l
 build_flags =
-  -I variants/m5stack_unit_c6l/repeater
   ${m5stack_unit_c6l.build_flags}
   ; LoRa settings - must match other devices on your mesh
   -D LORA_FREQ=910.525
@@ -104,7 +102,6 @@ build_flags =
   -D DISPLAY_HEIGHT=48
   -D DISPLAY_ROTATION=2
 build_src_filter = ${m5stack_unit_c6l.build_src_filter}
-  -<../variants/m5stack_unit_c6l/companion/*.cpp>
   +<helpers/ui/SSD1306SPIDisplay.cpp>
   +<../examples/simple_repeater>
   -<../examples/simple_repeater/UITask.cpp>
@@ -130,8 +127,6 @@ build_flags = ${m5stack_unit_c6l.build_flags}
   -D ROOM_PASSWORD='"hello"'
   -D MESH_PACKET_LOGGING=1
 build_src_filter = ${m5stack_unit_c6l.build_src_filter}
-  -<../variants/m5stack_unit_c6l/companion/*.cpp>
-  -<../variants/m5stack_unit_c6l/repeater/*.cpp>
   +<../examples/simple_room_server>
 lib_deps =
   ${m5stack_unit_c6l.lib_deps}

variants/m5stack_unit_c6l/companion/UITask.cpp

@@ -1,7 +1,7 @@
 // C6L-specific repeater UITask for 64x48 SSD1306 display
 // Replaces examples/simple_repeater/UITask.cpp via build_src_filter
 
-#include "UITask.h"
+#include "../../../examples/simple_repeater/UITask.h"
 #include <Arduino.h>
 #include <helpers/CommonCLI.h>
 #include <M5StackUnitC6LBoard.h>
@@ -26,11 +26,11 @@ void UITask::begin(NodePrefs* node_prefs, const char* build_date, const char* fi
   s_scroll_paused = true;
   _display->turnOn();
 
-  char *version = strdup(firmware_version);
+  char version[16];
+  strncpy(version, firmware_version, sizeof(version) - 1);
+  version[sizeof(version) - 1] = '\0';
   char *dash = strchr(version, '-');
-  if (dash) {
-    *dash = 0;
-  }
+  if (dash) *dash = '\0';
   sprintf(_version_info, "%s (%s)", version, build_date);
 }