fix: log warning when Windows key file permissions fail to set

Replace silently discarded icacls result with proper error handling
that logs a tracing::warn! on failure. Previously, if icacls failed
(binary not found, permission denied), the key file would remain
world-readable on Windows with no indication of the problem.

Closes #56

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/tools/browser.rs

@@ -366,6 +366,7 @@ impl BrowserTool {
 }
 
 #[async_trait]
+#[allow(clippy::too_many_lines)]
 impl Tool for BrowserTool {
     fn name(&self) -> &str {
         "browser"