fix: Add vendored OpenSSL for cross-compilation

- Add openssl dependency with vendored feature
- Fixes CI build for mips-unknown-linux-musl target
- Statically links OpenSSL instead of requiring system package
- Resolves openssl-sys build failures in cross-compile environment

Cargo.lock

@@ -271,6 +271,7 @@ dependencies = [
  "dotenvy",
  "futures",
  "mime_guess",
+ "openssl",
  "quick-xml",
  "rust-embed",
  "serde",
@@ -2174,6 +2175,15 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d05e27ee213611ffe7d6348b942e8f942b37114c00cc03cec254295a4a17852e"
 
+[[package]]
+name = "openssl-src"
+version = "300.5.5+3.5.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f1787d533e03597a7934fd0a765f0d28e94ecc5fb7789f8053b1e699a56f709"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "openssl-sys"
 version = "0.9.111"
@@ -2182,6 +2192,7 @@ checksum = "82cab2d520aa75e3c58898289429321eb788c3106963d0dc886ec7a5f4adc321"
 dependencies = [
  "cc",
  "libc",
+ "openssl-src",
  "pkg-config",
  "vcpkg",
 ]

backend/Cargo.toml

@@ -28,3 +28,4 @@ utoipa = { version = "5.4.0", features = ["axum_extras"] }
 utoipa-swagger-ui = { version = "9.0.2", features = ["axum"] }
 web-push = "0.10"
 base64 = "0.22"
+openssl = { version = "0.10", features = ["vendored"] }