audio: select the pipewire backend explicitly and ban the pulse one

Full-system audit findings: without an explicit provider selection the
image installed real PulseAudio (Plasma Mobile hard-path), which claims
the card and ships a wireplumber fragment disabling hardware.audio -
zero sinks forever. Mirror the dev phone's world: pipewire backend meta
+ pipewire-pulse + echo-cancel in extra_packages, pulse meta banned via
apk conflict in fp6-device-tweaks. The two hand-made /etc audio
fragments (wireplumber no-ACP rule, AEC pair for VoLTE speakerphone)
move into soc-fairphone-fp6-audio.

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

aports/device/fp6-device-tweaks/APKBUILD

@@ -11,12 +11,16 @@
 #    libssc crash on unconfigured SSC
 maintainer="Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>"
 pkgname=fp6-device-tweaks
-pkgver=2
+pkgver=3
 pkgrel=0
 pkgdesc="Fairphone 6 device-critical system configuration"
 url="https://forgejo.catcrafts.net/Catcrafts/fp6-img"
 arch="noarch"
 license="MIT"
+# apk-native ban: with this meta installed, the resolver routes Plasma
+# Mobile's audio through real PulseAudio, which claims the card and runs
+# wireplumber in a video-only profile - no sinks, ever
+depends="!postmarketos-base-ui-audio-backend-pulseaudio"
 options="!check"
 source="
 	inv-icm42600.conf