Switch musicdolphin from a Pi 4 to a Pi 5

The SD card moves over as is, so:
- pi_standard_setup can install the Pi 5 kernel (linux-image-rpi-2712, an arm64
  package on the armhf userland), which a Pi 4 image lacks. Opt-in via
  pi_standard_setup_install_pi5_kernel.
- The Pi is powered through the HiFiBerry board's GPIO header, so it cannot negotiate
  a 5A supply and would cap USB at 600mA. pi_hifiberry_amp sets
  usb_max_current_enable=1 when hifiberry_powers_pi is true (default false).
- The DHT22 poller is off: Adafruit_DHT bit-bangs BCM283x registers, which the Pi 5
  no longer has (GPIO sits behind the RP1 chip).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

roles/pi_hifiberry_amp/README.md

@@ -3,4 +3,7 @@
 Deactivates the Pi's onboard analog audio and activates a HiFiBerry
 amp/DAC overlay instead.
 
-**Key vars:** `hifiberry_overlay`
+**Key vars:** `hifiberry_overlay`, `hifiberry_powers_pi`
+
+`hifiberry_powers_pi` (default `false`) is for a Pi fed through the HiFiBerry board's
+GPIO header. On a Pi 5 that sets `usb_max_current_enable=1`, or USB is capped at 600mA.