Improve error message for missing franc-min dependency

[Copilot]

The error handler for missing franc-min logged "franc-min not available, using feed-declared language only" without telling users how to fix it.

Changes

• Enhanced error message to include actionable resolution steps
• Message now explicitly instructs users to run npm install when the package is missing

} catch (e) {
  console.error('WARNING: franc-min package not found. Language detection will be limited to feed-declared languages only.');
  console.error('To enable automatic language detection, please run: npm install');
  detectLang = () => null;
}

This addresses the review feedback that error messages should be informative and include instructions for resolution.

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