Add dark color scheme, backlight timeout, and L/R swap feature

- Invert UI colors: black background with white text, yellow highlights
- Add 30-second backlight timeout with auto-wake on button press
- Add Swap L/R menu option with checkbox to swap audio channels
- Update volume page styling (yellow bar, full-screen container)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

main/bt_app.c

@@ -35,7 +35,7 @@
 
 /* device name */
 #define TARGET_DEVICE_NAME    "ESP_SPEAKER"
-#define LOCAL_DEVICE_NAME     "ESP_A2DP_SRC"
+#define LOCAL_DEVICE_NAME     "SOUNDSHOT"
 
 /* AVRCP used transaction label */
 #define APP_RC_CT_TL_GET_CAPS            (0)
@@ -798,6 +798,8 @@ void generate_exp(uint8_t *buf, int len, float balance)
     //float rate_hz = MIN_RATE_HZ * powf(MAX_RATE_HZ / MIN_RATE_HZ, abs_balance);
     float samples_per_click = SAMPLE_RATE / rate_hz;
 
+    bool swap_lr = system_getSwapLR();
+
     for (int i = 0; i < samples_needed; i++) {
         int16_t left = 0;
         int16_t right = 0;
@@ -814,8 +816,13 @@ void generate_exp(uint8_t *buf, int len, float balance)
 
         click_timer -= 1.0f;
 
-        samples[i * 2 + 0] = left;
-        samples[i * 2 + 1] = right;
+        if (swap_lr) {
+            samples[i * 2 + 0] = right;
+            samples[i * 2 + 1] = left;
+        } else {
+            samples[i * 2 + 0] = left;
+            samples[i * 2 + 1] = right;
+        }
 
     }
 }