Fix SEO dashboard overview URL resolution and audit empty states

[AJaySi]

Motivation

• Prevent querying the backend with an incorrect hardcoded site URL and let the backend derive the truth-of-record (onboarding SSOT), and make the audit UI show clear states when the site is not configured or has no audited pages.

Description

• Remove the hardcoded https://alwrity.com fallback and initialize websiteUrl as null in the dashboard data loader.
• Call /api/seo-dashboard/overview without a site_url param by default and only pass site_url when an explicit selectedSiteUrl is present, avoiding wrong-site queries.
• Resolve site URL in priority order: response.data.website_url from the overview response, then the authenticated userDataAPI.getWebsiteURL() fallback, otherwise remain unconfigured.
• Update technical audit empty-state alerts to present the clearer messages: Audit scheduled, No pages audited yet, and Site not configured.

Testing

• Attempted lint via npm run eslint but the project has no eslint script so the lint step could not run in this environment.
• Attempted build via npm run build but the build failed due to missing react-scripts/frontend dependencies in the environment.
• Attempted tests via npm test but test execution failed because react-scripts is not available here.
• Attempted a Playwright screenshot of http://localhost:3000/seo-dashboard which failed with ERR_EMPTY_RESPONSE because the frontend server was not running in this environment.

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Codex Task