Fix build success detection + minimizable build window + de-dupe event logs

- build_sln now trusts UnrealBuildTool's "Result: Succeeded" (and absence of
  real compile errors) over MSBuild's exit code, which is non-zero for a side
  project even when the UE game module built fine.
- Fixed double event-listener registration (async unlisten under StrictMode)
  that duplicated every p4-log / p4-transfer / build-log line.
- Build overlay can be minimized to a small floating chip (spinner while
  building, ✓/✗ when done), click to expand, × to dismiss.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -762,9 +762,25 @@ async fn build_sln(path: String) -> Result<String, String> {
         }
     };
 
+    // For Unreal, the .sln drives UnrealBuildTool; MSBuild can return non-zero for a
+    // side project even when UBT reports the game module built fine. So trust UBT's
+    // "Result: Succeeded" (and the absence of real compile errors) over the exit code.
+    let mut ubt_result = false;
+    let mut ubt_success = false;
+    let mut compile_error = false;
+    let mut scan = |line: &str| {
+        let l = line.to_ascii_lowercase();
+        if l.contains("result: succeeded") { ubt_result = true; ubt_success = true; }
+        if l.contains("result: failed") { ubt_result = true; }
+        if l.contains(": error ") || l.contains(") error ") || l.contains("error msb") {
+            compile_error = true;
+        }
+    };
+
     if let Some(out) = child.stdout.take() {
         for line in BufReader::new(out).lines().map_while(Result::ok) {
             if !line.trim().is_empty() {
+                scan(&line);
                 emit(line, false, false);
             }
         }
@@ -775,11 +791,17 @@ async fn build_sln(path: String) -> Result<String, String> {
         let _ = std::io::Read::read_to_string(&mut se, &mut buf);
         for line in buf.lines() {
             if !line.trim().is_empty() {
+                scan(line);
                 emit(line.to_string(), false, false);
             }
         }
     }
-    let ok = status.success();
+    // UBT verdict wins when present; otherwise fall back to MSBuild's exit code
+    let ok = if ubt_result {
+        ubt_success && !compile_error
+    } else {
+        status.success()
+    };
     emit(if ok { "✓ Build succeeded.".into() } else { "✗ Build FAILED.".into() }, true, ok);
     if ok {
         Ok("ok".into())