refactor(macos): centralize process pipe draining

apps/macos/Sources/Clawdbot/Process+PipeRead.swift

@@ -0,0 +1,11 @@
+import Foundation
+
+extension Process {
+    /// Runs the process and drains the given pipe before waiting to avoid blocking on full buffers.
+    func runAndReadToEnd(from pipe: Pipe) throws -> Data {
+        try self.run()
+        let data = pipe.fileHandleForReading.readToEndSafely()
+        self.waitUntilExit()
+        return data
+    }
+}