idle: add IDLE_SLEEP_WHEN_CHARGING and IDLE_WAKE_ON_TOUCH

Addresses review feedback on #24:

- New config IDLE_SLEEP_WHEN_CHARGING (default false): while USB is
  plugged in we don't enter sleep and we wake immediately if power
  comes back. Covers both "I like watching Clawd animations on my
  plugged-in desk device" and "alternative hardware without a battery
  is always on USB, sleep would be odd."

- New config IDLE_WAKE_ON_TOUCH (default true): a touch on the dark
  panel wakes the device. The first touch is swallowed (mirrors the
  button wake-consumption), so tapping a dark screen wakes without
  also toggling splash<->usage. Set false to keep the original
  pets/sleeves-safe behaviour where touch is fully ignored while
  asleep.

power.{h,cpp} grow a power_is_vbus_in() helper backed by
pmu.isVbusIn() — distinct from isCharging() so the no-battery case
("plugged in, nothing to charge") is detected correctly.

firmware/src/idle.cpp

@@ -2,6 +2,7 @@
 #include "idle.h"
 #include "idle_cfg.h"
 #include "display_cfg.h"   // declares `extern Arduino_CO5300 *gfx;`
+#include "power.h"
 
 enum IdleState {
     STATE_AWAKE,
@@ -69,6 +70,16 @@ bool idle_is_asleep(void) {
 void idle_tick(void) {
     uint32_t now = millis();
 
+    // While on USB power (if configured), don't sleep — and wake from sleep
+    // when power comes back. Treats USB-in as continuous activity.
+    if (!IDLE_SLEEP_WHEN_CHARGING && power_is_vbus_in()) {
+        last_activity_ms = now;
+        if (state == STATE_ASLEEP || state == STATE_FADING_OUT) {
+            begin_fade(DISPLAY_DEFAULT_BRIGHTNESS, now);
+            state = STATE_FADING_IN;
+        }
+    }
+
     switch (state) {
     case STATE_AWAKE:
         if (now - last_activity_ms >= IDLE_TIMEOUT_MS) {

firmware/src/idle_cfg.h

@@ -9,3 +9,15 @@
 #define IDLE_FADE_STEP_MS           20       // tick interval per fade step
 
 #define DISPLAY_DEFAULT_BRIGHTNESS  200      // active-screen brightness
+
+// When false, the device never enters sleep while USB power is present (also
+// wakes from sleep when USB is plugged back in). Useful when sitting on a
+// desk plugged in — also covers battery-less hardware that's always on USB.
+// Set true to sleep regardless of power source.
+#define IDLE_SLEEP_WHEN_CHARGING    false
+
+// When true, a touch on the dark panel wakes the device (first touch is
+// consumed for wake only, second touch acts normally). When false, touch is
+// fully ignored during sleep — useful if cats/sleeves brushing the panel
+// overnight would be a problem.
+#define IDLE_WAKE_ON_TOUCH          true

firmware/src/main.cpp

@@ -55,11 +55,36 @@ static void touch_read() {
         touch_pressed = false;
     }
 
-    // Touch never counts as user activity and is fully swallowed while the
-    // panel is dark — avoids accidental wakes and prevents LVGL from secretly
-    // toggling splash<->usage behind a black screen.
+    // Touch policy is driven by IDLE_WAKE_ON_TOUCH:
+    //   true  → a press edge while asleep wakes the device and the first
+    //           touch is swallowed (mirrors the button wake-consumption); a
+    //           press while awake counts as activity.
+    //   false → touch never counts as activity and is fully swallowed while
+    //           the panel is dark, so pets/sleeves can't wake it overnight
+    //           and LVGL can't quietly toggle splash<->usage on a black panel.
+    if (IDLE_WAKE_ON_TOUCH) {
+        static bool touch_was = false;
+        static bool touch_wake_swallowed = false;
+        bool touch_now = touch_pressed;
+        if (touch_now && !touch_was) {
+            if (idle_consume_wake_press()) {
+                touch_wake_swallowed = true;
+                touch_pressed = false;  // hide this press from LVGL
+            }
+        } else if (!touch_now && touch_was) {
+            if (touch_wake_swallowed) {
+                touch_wake_swallowed = false;
+                touch_pressed = false;  // also hide the corresponding release
+            }
+        } else if (touch_now && touch_wake_swallowed) {
+            // Held finger through wake — keep hiding until release.
+            touch_pressed = false;
+        }
+        touch_was = touch_now;
+    } else {
         if (idle_is_asleep()) touch_pressed = false;
     }
+}
 
 // ---- LVGL draw buffers (PSRAM-backed, partial render) ----
 #define BUF_LINES 40

firmware/src/power.cpp

@@ -8,6 +8,7 @@
 
 static int      cached_pct      = -1;
 static bool     cached_charging = false;
+static bool     cached_vbus     = false;
 static bool     pwr_pressed_flag = false;
 static uint32_t last_battery_ms  = 0;
 static uint32_t last_charging_ms = 0;
@@ -30,6 +31,7 @@ void power_init(void) {
     pmu.enableIRQ(XPOWERS_AXP2101_PKEY_SHORT_IRQ);
 
     cached_charging = pmu.isCharging();
+    cached_vbus     = pmu.isVbusIn();
     cached_pct = pmu.getBatteryPercent();
 }
 
@@ -39,6 +41,7 @@ void power_tick(void) {
     if (now - last_charging_ms >= CHARGING_POLL_MS) {
         last_charging_ms = now;
         cached_charging = pmu.isCharging();
+        cached_vbus     = pmu.isVbusIn();
     }
 
     if (now - last_battery_ms >= BATTERY_POLL_MS) {
@@ -65,6 +68,10 @@ bool power_is_charging(void) {
     return cached_charging;
 }
 
+bool power_is_vbus_in(void) {
+    return cached_vbus;
+}
+
 bool power_pwr_pressed(void) {
     if (pwr_pressed_flag) {
         pwr_pressed_flag = false;

firmware/src/power.h

@@ -4,4 +4,5 @@ void power_init(void);
 void power_tick(void);
 int  power_battery_pct(void);    // 0-100, or -1 if no battery
 bool power_is_charging(void);
+bool power_is_vbus_in(void);     // USB cable present (true even with no battery)
 bool power_pwr_pressed(void);    // true once per AXP2101 PWR button short-press