Release: build a static ARMv7 (armhf) Linux agent

Adds armv7-unknown-linux-musleabihf to both release pipelines: the archive,
a .deb for armhf and an Arch package for armv7h. Agent and CLI only, like the
other non-x86_64 Linux builds.

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

dist/arch/build-pkg.sh

@@ -4,7 +4,7 @@
 #
 # Usage: build-pkg.sh <binary> <arch> <version> <output.pkg.tar.zst> [tray_binary]
 #   <binary>      path to the built tsunagi (agent/CLI) executable
-#   <arch>        pacman architecture: x86_64 or aarch64
+#   <arch>        pacman architecture: x86_64, aarch64 or armv7h
 #   <version>     package version (the tag without its leading v)
 #   <output>      path to write the package to
 #   [tray_binary] optional tsunagi-tray GUI executable; when given, the package

dist/deb/build-deb.sh

@@ -4,7 +4,7 @@
 #
 # Usage: build-deb.sh <binary> <deb_arch> <version> <output.deb> [tray_binary]
 #   <binary>      path to the built tsunagi (agent/CLI) executable
-#   <deb_arch>    Debian architecture: amd64 or arm64
+#   <deb_arch>    Debian architecture: amd64, arm64 or armhf
 #   <version>     package version (the tag without its leading v)
 #   <output>      path to write the .deb to
 #   [tray_binary] optional path to the tsunagi-tray GUI executable; when given,