Document and apply coding standards

Caldova Careers should model maintainable code for workshop learners. Add lightweight standards for comments, exported functions, and component props, then apply them to the existing codebase.

Acceptance criteria

• Comments explain intent or constraints, not mechanics that are obvious from the code.
• Exported functions in db/ and src/lib/ have useful TSDoc.
• .astro components with props document their Props shape.
• The README links to the coding standards.
• Existing code is updated where it falls short of the standards.
• npm run lint passes.

Start by reviewing the existing code in db/, src/lib/, and the .astro components, then inspect the README and run npm run lint. Define the coding standards from the acceptance criteria, document them, link them from the README, and update existing comments, exported functions, and component Props documentation until lint passes.