fix: SDK Agent fails on Windows when username contains spaces (#1022)

* fix: SDK Agent fails on Windows when username contains spaces

Fixes spawn failure on Windows when the user's path contains spaces
(e.g., C:\Users\Anderson Wang\).

Root cause:
- SDKAgent.ts returns full auto-detected path with spaces
- ProcessRegistry.ts cannot execute .cmd files when path contains spaces

Solution:
- SDKAgent: On Windows, prefer "claude.cmd" via PATH instead of full path
- ProcessRegistry: Use cmd.exe /d /c wrapper for .cmd files on Windows

This preserves argument boundaries (e.g., empty string values) while
properly handling paths with spaces.

Fixes #1014

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* docs: add Windows spawn path with spaces fix documentation

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/services/worker/SDKAgent.ts

@@ -446,7 +446,17 @@ export class SDKAgent {
       return settings.CLAUDE_CODE_PATH;
     }
 
-    // 2. Try auto-detection
+    // 2. On Windows, prefer "claude.cmd" via PATH to avoid spawn issues with spaces in paths
+    if (process.platform === 'win32') {
+      try {
+        execSync('where claude.cmd', { encoding: 'utf8', windowsHide: true, stdio: ['ignore', 'pipe', 'ignore'] });
+        return 'claude.cmd'; // Let Windows resolve via PATHEXT
+      } catch {
+        // Fall through to generic error
+      }
+    }
+
+    // 3. Try auto-detection for non-Windows platforms
     try {
       const claudePath = execSync(
         process.platform === 'win32' ? 'where claude' : 'which claude',