fix(macos): drop codesign_identity:None from py2app options

The py2app version on macos-15 runners rejects codesign_identity with
"command 'py2app' has no such option 'codesign_identity'". Setting it
to None was already a no-op — signing happens in
scripts/macos_sign_and_notarize.sh — so just omit the key entirely.

Resolves the only remaining failing check on PR #10 (build job ran as
continue-on-error, so PR was already mergeable; this turns the canary
green).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: JosephOIbrahim

setup_py2app.py

@@ -82,9 +82,10 @@
     ],
     "strip": False,
     "optimize": 0,
-    # We sign in a separate step. py2app's signer is too coarse
-    # for our entitlements requirements.
-    "codesign_identity": None,
+    # Signing is handled by scripts/macos_sign_and_notarize.sh in a
+    # separate step (py2app's signer is too coarse for our entitlements
+    # requirements). Omitting codesign_identity entirely — older py2app
+    # versions reject the option even when set to None.
 }
 
 # Architecture: opt-in to universal2 only when explicitly requested