feat: Add sal-net package to workspace

- Add new sal-net package to the workspace.
- Update MONOREPO_CONVERSION_PLAN.md to reflect the
  addition of the sal-net package and mark it as
  production-ready.
- Add Cargo.toml and README.md for the sal-net package.

os/src/package.rs

@@ -420,12 +420,43 @@ mod tests {
 
     #[test]
     fn test_platform_detection() {
-        // This test will return different results depending on the platform it's run on
+        // Test that platform detection returns a valid platform
         let platform = Platform::detect();
         println!("Detected platform: {:?}", platform);
 
-        // Just ensure it doesn't panic
-        assert!(true);
+        // Verify that we get one of the expected platform values
+        match platform {
+            Platform::Ubuntu | Platform::MacOS | Platform::Unknown => {
+                // All valid platforms
+            }
+        }
+
+        // Test that detection is consistent (calling it twice should return the same result)
+        let platform2 = Platform::detect();
+        assert_eq!(platform, platform2);
+
+        // Test that the platform detection logic makes sense for the current environment
+        match platform {
+            Platform::MacOS => {
+                // If detected as macOS, sw_vers should exist
+                assert!(std::path::Path::new("/usr/bin/sw_vers").exists());
+            }
+            Platform::Ubuntu => {
+                // If detected as Ubuntu, lsb-release should exist and contain "Ubuntu"
+                assert!(std::path::Path::new("/etc/lsb-release").exists());
+                if let Ok(content) = std::fs::read_to_string("/etc/lsb-release") {
+                    assert!(content.contains("Ubuntu"));
+                }
+            }
+            Platform::Unknown => {
+                // If unknown, neither macOS nor Ubuntu indicators should be present
+                // (or Ubuntu file exists but doesn't contain "Ubuntu")
+                if std::path::Path::new("/usr/bin/sw_vers").exists() {
+                    // This shouldn't happen - if sw_vers exists, it should be detected as macOS
+                    panic!("sw_vers exists but platform detected as Unknown");
+                }
+            }
+        }
     }
 
     #[test]