Fix Oura login and Electron activation crash

[seddm-sketch]

Summary

Fixes two runtime issues found while using the packaged macOS app:

• The Oura login automation failed when the authentication choice screen showed both “Use passkey” and “Email me a code”.
• The Electron app could crash on macOS activation because mainWindow.show() was called before mainWindow had been initialized.

Root Cause

Oura’s auth screen now renders multiple button[name="selectedId"] buttons. The login automation used that broad locator directly, which caused Playwright strict mode to fail because it matched both the passkey and email-code buttons.

Electron also declared mainWindow without an initial value. On macOS, the activate event can fire while mainWindow is still undefined, causing an uncaught exception when calling .show().

Changes

• Explicitly select the email-code authentication button using accessible button text, with a fallback to the outlined selectedId button.
• Use .first for OTP input locators to avoid strict-mode ambiguity.
• Initialize mainWindow to null.
• Add a shared showOrCreateWindow() helper for macOS activation and tray open actions.

Verification

• Confirmed Oura email-code login proceeds past the auth choice screen.
• Rebuilt the macOS DMG and confirmed the app opens without the previous uncaught Electron exception.
• Ran:

python3 -m compileall backend/src/automation.py
cd frontend && npx tsc -p electron/tsconfig.json