fix(xurl): treat PermissionError from PATH lookup as unavailable (#322)

is_available() only caught FileNotFoundError and TimeoutExpired. On WSL,
a /mnt/c/.../WindowsApps entry on $PATH returns EACCES during exec, and
Python raises PermissionError. That escaped is_available() and crashed
pipeline.diagnose() before any source ran.

Catch OSError instead. It covers FileNotFoundError, PermissionError, and
any other spawn-time OS error, so a non-executable xurl on PATH falls
through to the next backend instead of aborting the run.

skills/last30days/scripts/lib/xurl_x.py

@@ -46,9 +46,10 @@ def is_available() -> bool:
             timeout=10,
         )
         return result.returncode == 0 and '"username"' in result.stdout
-    except FileNotFoundError:
-        return False
-    except subprocess.TimeoutExpired:
+    except (OSError, subprocess.TimeoutExpired):
+        # OSError covers FileNotFoundError (no xurl on PATH) and
+        # PermissionError (a non-executable match on PATH, e.g. WSL's
+        # /mnt/c/.../WindowsApps shim returning EACCES on exec).
         return False