fix: provide fallback values for undefined runtime config

[danielroe]

🔗 Linked issue

nuxt/nuxt#18586

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This provides fallback values for undefined runtime config: nuxt/nuxt#18586 (review)

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #907 (20c1d2c) into main (f7eed65) will increase coverage by 0.03%.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##             main     #907      +/-   ##
==========================================
+ Coverage   67.50%   67.53%   +0.03%     
==========================================
  Files          59       59              
  Lines        5866     5878      +12     
  Branches      637      641       +4     
==========================================
+ Hits         3960     3970      +10     
- Misses       1897     1899       +2     
  Partials        9        9              

Impacted Files	Coverage Δ
src/utils/index.ts	54.22% <90.00%> (+1.34%)	⬆️
src/options.ts	88.88% <100.00%> (+0.06%)	⬆️

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[pi0]

Thanks <3