fix(platform): use cross-platform hostname helper for Windows builds

Replace direct nix::unistd::gethostname() calls with a platform helper
that uses COMPUTERNAME env var on Windows and nix on Unix.

Author: m3nu

crates/vger-core/src/commands/backup.rs

@@ -1732,9 +1732,7 @@ pub fn run_with_progress(
         let time_end = Utc::now();
 
         // Build snapshot metadata
-        let hostname = nix::unistd::gethostname()
-            .map(|h| h.to_string_lossy().to_string())
-            .unwrap_or_else(|_| "unknown".into());
+        let hostname = crate::platform::hostname();
         let username = std::env::var("USER").unwrap_or_else(|_| "unknown".into());
 
         let snapshot_meta = SnapshotMeta {

crates/vger-core/src/platform/mod.rs

@@ -1,2 +1,17 @@
 pub mod fs;
 pub mod shell;
+
+/// Return the system hostname, or `"unknown"` if it cannot be determined.
+pub fn hostname() -> String {
+    #[cfg(unix)]
+    {
+        nix::unistd::gethostname()
+            .map(|h| h.to_string_lossy().to_string())
+            .unwrap_or_else(|_| "unknown".into())
+    }
+
+    #[cfg(windows)]
+    {
+        std::env::var("COMPUTERNAME").unwrap_or_else(|_| "unknown".into())
+    }
+}

crates/vger-core/src/repo/lock.rs

@@ -39,9 +39,7 @@ impl LockGuard {
 
 /// Acquire an advisory lock on the repository.
 pub fn acquire_lock(storage: &dyn StorageBackend) -> Result<LockGuard> {
-    let hostname = nix::unistd::gethostname()
-        .map(|h| h.to_string_lossy().to_string())
-        .unwrap_or_else(|_| "unknown".into());
+    let hostname = crate::platform::hostname();
     let pid = std::process::id() as u64;
 
     // Prefer backend-native lock APIs when available (e.g. REST server locks).