ci(release): build Linux artifacts as static musl binaries (#447)

Build Linux release artifacts as statically linked musl binaries for x86_64 and aarch64, update packaging and updater handling, and document the reduced runtime requirements.

Keep release version preparation locked without refreshing dependencies or committing Cargo.lock.

Closes #440

README.md

@@ -117,6 +117,12 @@ For more information or other platforms, please visit [termscp.rs](https://terms
 
 ### Requirements ❗
 
+The official Linux binaries and `.deb` packages are statically linked against
+musl and have **no runtime requirements**: they run on any distribution and
+any glibc version.
+
+These are only required to build termscp from source:
+
 - **Linux** users:
   - libdbus-1
   - pkg-config