The app can run on web in two modes:
1. WordPress embedded: initialProps injected by woocommerce-pos plugin
2. Standalone: User connects to a site manually via the auth flow

This commit fixes three issues that broke standalone mode:

1. initialProps detection: Changed from exporting empty object {} to
   exporting null when no valid WordPress props are present. An empty
   object was truthy, causing hydration steps to execute incorrectly.

2. Hydration step conditions: Updated shouldExecute checks to verify
   initialProps?.site exists rather than just truthy initialProps.
   This ensures processInitialPropsStep and testAuthorizationStep
   are properly skipped in standalone mode.

3. Web logout: In standalone mode, logout now properly clears the
   session state (like native does) instead of just reloading the page.
   Previously, reloading kept the user logged in since IndexedDB
   persisted the session.

Tests verify:
- Returns null when globalThis.initialProps is undefined
- Returns null for empty object {}
- Returns null when missing required site property
- Returns null when missing required wp_credentials property
- Returns frozen object when valid WordPress props exist

Also:
- Add testing-requirements rule to .cursor/rules
- Fix .gitignore to properly include .cursor/rules/

- Add lint job to test.yml that runs before unit tests
- Update testing-requirements.mdc to include linting requirements
- Pre-commit checklist: run pnpm lint:fix, then pnpm test

The lint job uses the existing @wcpos/eslint-config which includes:
- Prettier (tabs, single quotes, trailing commas)
- Import ordering rules
- React Compiler rules

Run `pnpm lint:fix` to auto-fix formatting and import ordering issues.

Manual fixes:
- Extract `navigateToUrl()` helper in app-state/index.tsx to fix
  React Compiler warning about window.location.href assignment
- Extract `navigateToUrl()` helper in use-wcpos-auth/index.web.ts
- Remove unused `appLogger` import in app-state/index.tsx

Note: Some pre-existing lint errors remain that require larger refactoring:
- React Compiler mutation warnings (ui-settings-form files)
- Module resolution issues (styled-components, expo modules)
- Unescaped entities in error messages
- Conditional hooks in some components

These should be addressed in separate PRs.