feat(oled): charge ETA, persistent lightbar, charging-aware idle ladder

Status screen: show an estimated time-to-full ("~43m") while charging,
self-calibrating from each 10% battery notch with Li-ion taper correction
(discard the partial plug-in step; 3-sample moving average; per-step weight
1.0/1.5/2.2 for bulk/80-90/90-100%). Shows "~--m" until the first full step.

Lightbar: the chosen mode + 4 favorites now persist to config flash and
stick across every screen (and through gameplay/audio). A single
lightbar_service() owns the LED via the persistent state[] block (new
state_set_led/state_get_led) with a host-override gate (g_lightbar_override)
so the host's AllowLedColor can't stomp a firmware-chosen mode. New HOST
passthrough mode (default) keeps the game in control of the LED out of the
box. The charging amber pulse (255,100,0) is folded in as top priority.

Idle ladder: keep the panel at the dim/dot tier (never full-off) while
charging so users stop unplugging to wake it (which reset the charge ETA).
Fix idle detection to deadzone stick jitter [120,140] + skip the counter
byte (idata[6]) so the dot tier engages with a controller connected
(mirrors bt.cpp's inactivity heuristic).

New Config_body fields: lightbar_mode + lb_fav_{r,g,b}[4].

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/config.cpp

@@ -95,6 +95,12 @@ void config_valid() {
         body->auto_haptics_lowpass = 1; // 160 Hz
         printf("[Config] auto_haptics_lowpass invalid, defaulting to 1 (160 Hz)\n");
     }
+    if (body->lightbar_mode > 8) { // 0..7 OLED modes + 8 = HOST passthrough (default)
+        body->lightbar_mode = 8;
+        printf("[Config] lightbar_mode invalid, defaulting to 8 (HOST passthrough)\n");
+    }
+    // lb_fav_{r,g,b} need no validation — any 0..255 is a legal color, and an
+    // erased flash sector (0xFF) yields 4 white favorites, a usable default.
     if (body->config_version != CONFIG_VERSION) {
         body->config_version = CONFIG_VERSION;
         printf("[Config] Warning: Config may breaking change\n");