feat: flashlight - the whole screen white at full brightness

L2: a Flashlight app on Home (a lightbulb icon added to the fonts): a
white layer over everything, the backlight at 100 %, no auto-off; a tap,
the side or the top button puts it away and the brightness back.
L1: Tools > System > Flashlight, the whole OLED lit at full contrast
until a key. Not on e-ink.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/solo/tools.md

@@ -8,7 +8,7 @@ home page.
 
 > [!NOTE]
 > **Wio Tracker L2:** the tools are apps on the home screen: Messages, Nodes,
-> Settings, Compass, Clock, GPS, Bot, Repeater, Admin, Diagnostics. The trail,
+> Settings, Compass, Clock, GPS, Bot, Repeater, Admin, Diagnostics, Flashlight. The trail,
 > live sharing and the locator are on the map (its tools button) and in
 > Settings › Map.
 
@@ -90,6 +90,16 @@ single contact or channel from its options.
 > [!NOTE]
 > **Wio Tracker L2:** the melody editor is under Settings › Sound.
 
+## Flashlight
+
+**Tools › System › Flashlight** lights the whole screen white at full
+brightness and keeps it on until you press a key; the brightness goes back
+when you leave. Not on e-ink, which gives no light.
+
+> [!NOTE]
+> **Wio Tracker L2:** the Flashlight app. A tap, the side button or the top
+> button puts it away.
+
 ## Status
 
 The **Status** home page sums up the radio, GPS, battery and mesh in four