docs: update repository coding standards

[alng20]

Description

Consistent commenting and documentation standards make it easier to review changes and keep the codebase understandable. This update clarifies that comments should explain intent rather than restate code, and defines documentation contracts for exported data-layer functions and reusable Astro component props.

Related Issue

Fixes: #8

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📚 Documentation update
• 🧪 Test update
• 🔧 Refactor (no functional changes)

Changes Made

• Added shared comment philosophy and TypeScript formatting standards.
• Documented TSDoc expectations for exported functions in db/ and src/lib/, including the injectable database parameter.
• Added documentation expectations for reusable Astro component Props interfaces.
• Enforced TypeScript indentation, single quotes, and semicolons in ESLint while preserving the existing Playwright indentation style.
• Linked the standards from the README and Copilot instructions.

Testing

Data Layer Changes

N/A - no data-layer code or schema changes.

Frontend Changes

N/A - no UI changes.

npm run lint passes. git diff --check is clean.

Checklist

• My code follows the project's coding standards
• I have used explicit TypeScript types for function parameters and return values
• I have built the UI with Astro components and Tailwind CSS utility classes (dark theme)
• I have updated documentation (README, instruction files) if needed
• My changes are focused on a single concern
• I have written clear commit messages explaining what and why

Additional Notes

N/A