powerbread: drop unused pb_ui_get_mode, include errno.h explicitly

Final-review cleanup: both optional recommendations from the whole-branch
review.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: rosterloh

applications/powerbread/src/shell.c

@@ -7,6 +7,7 @@
 #include "sampler.h"
 #include "ui.h"
 
+#include <errno.h>
 #include <stdlib.h>
 #include <string.h>
 

applications/powerbread/src/ui.c

@@ -44,11 +44,6 @@ void pb_ui_set_mode(enum pb_mode mode)
 	}
 }
 
-enum pb_mode pb_ui_get_mode(void)
-{
-	return (enum pb_mode)atomic_get(&req_mode);
-}
-
 void pb_ui_step_mode(int dir)
 {
 	int m = ((int)atomic_get(&req_mode) + dir + PB_MODE_COUNT) % PB_MODE_COUNT;

applications/powerbread/src/ui.h

@@ -18,7 +18,6 @@ enum pb_mode {
 
 int pb_ui_init(void);
 void pb_ui_set_mode(enum pb_mode mode);
-enum pb_mode pb_ui_get_mode(void);
 void pb_ui_step_mode(int dir);
 void pb_ui_set_channel(uint8_t ch);
 uint8_t pb_ui_get_channel(void);