v0.5.1: static musl builds for OpenWRT (amd64 + arm64)

A user on OpenWRT x86_64 reported the linux release doesn't run there —
root cause was glibc vs musl mismatch (our gnu binary was looking for a
dynamic linker that doesn't exist on router userlands). Add two musl
targets that produce fully static PIE binaries:

- x86_64-unknown-linux-musl  -> mhrv-rs-linux-musl-amd64.tar.gz
- aarch64-unknown-linux-musl -> mhrv-rs-linux-musl-arm64.tar.gz

CI uses the messense/rust-musl-cross docker images (better-maintained
than cargo-zigbuild with a pinned zig, which has version regressions
on the ar wrapper between 0.13 and 0.16).

Locally verified:
- both archs cross-compile green in docker
- resulting x86_64 binary (3.3 MB) runs in an alpine:latest container,
  --version / --help work, no dynamic lib requirements

The musl archive skips the UI (routers are headless) and swaps run.sh
for a procd init script (assets/openwrt/mhrv-rs.init) expecting the
binary at /usr/bin/mhrv-rs and config at /etc/mhrv-rs/config.json.

Side effect: switched tokio-rustls to default-features=false + ring
(was pulling aws-lc-rs transitively, which can't easily cross-compile
for musl). The main crate already uses ring explicitly, so no runtime
behavior change.

README gets a 'Running on OpenWRT (or any musl distro)' section in
both English and Persian with scp + procd enable/start recipe.
Closes #2.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mhrv-rs"
-version = "0.5.0"
+version = "0.5.1"
 edition = "2021"
 description = "Rust port of MasterHttpRelayVPN -- DPI bypass via Google Apps Script relay with domain fronting"
 license = "MIT"
@@ -24,7 +24,7 @@ ui = ["dep:eframe"]
 
 [dependencies]
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "net", "time", "io-util", "signal", "sync"] }
-tokio-rustls = "0.26"
+tokio-rustls = { version = "0.26", default-features = false, features = ["ring", "tls12"] }
 rustls = { version = "0.23", default-features = false, features = ["ring", "std", "tls12"] }
 rustls-pemfile = "2"
 webpki-roots = "0.26"