Add configurable battery and USB display behavior

Persist separate display modes and timeouts in seconds for battery and USB power, expose four controls in WebConfig and CLI, and apply one shared policy across display-equipped roles.

Detect R8 external power from a USB host or calibrated battery voltage above 4.21 V, with cached sampling and hysteresis. Add policy, persistence, browser, and R8 power-detection regression coverage.

docs/cli_command_availability.md

@@ -268,7 +268,8 @@ should use command `0x42`. See [Companion radio binary protocol](companion_proto
 | Operational | [`advert`](cli_commands.md#send-a-flood-advert) | Advert-capable role | Yes | Yes | Yes | Yes | Yes |
 | Operational | [`advert.zerohop`](cli_commands.md#send-a-zero-hop-advert) | Advert-capable role | Yes | Yes | Yes | Yes | Yes |
 | Operational | [`erase`](cli_commands.md#erasefactory-reset) | Local connection | Local | Local | Local | Local | Local |
-| Display | [`get/set display.timeout`; `get/set display.flip`](cli_commands.md#set-mqtt-observer-display-timeout-and-flip) | MQTT observer with display; flip needs a supported driver | No | No | No | Feature | No |
+| Display | [`get/set display.mode`; `display.timeout`; `display.usb.mode`; `display.usb.timeout`](cli_commands.md#set-display-modes-and-timeouts) | Display-equipped roles; pairing modes require BLE Companion | Feature | Feature | Feature | Feature | Feature |
+| Display | [`get/set display.flip`](cli_commands.md#set-mqtt-observer-display-flip) | MQTT observer with supported display driver | No | No | No | Feature | No |
 | Information | [`ver`](cli_commands.md#get-the-version) | All text CLI roles | Yes | Yes | Yes | Yes | Yes |
 | Information | [`board`](cli_commands.md#show-the-hardware-name) | All text CLI roles | Yes | Yes | Yes | Yes | Yes |
 | Diagnostics | [`get storage.layout`](cli_commands.md#show-the-storage-layout) | Detected flash size and live partition table | Yes | Yes | Yes | Yes | Yes |