[JSDoc] Add JSDoc Examples and Return Contracts in lib/money.ts

• Labels: good first issue, documentation, difficulty:beginner, area:core
• Target File: src/lib/money.ts
• Estimated Time: 10–15 minutes
• Difficulty: Level 2 (Beginner)

Why This Matters

src/lib/money.ts contains PACT's core currency math utilities. Comprehensive JSDoc comments with @example, @param, and @returns tags provide instant in-editor documentation for other developers.

Current Behavior

Several utility functions in src/lib/money.ts (such as formatCentsToCurrency and dollarsToCents) have brief comments but lack structured JSDoc @example blocks.

Requested Change

Add formatted JSDoc docstrings with @param, @returns, and @example blocks above dollarsToCents and formatCentsToCurrency in src/lib/money.ts.

Acceptance Criteria

• Structured JSDoc docstrings added above the specified functions in src/lib/money.ts.
• Examples accurately demonstrate integer cents inputs and outputs.
• npx tsc --noEmit and npm run lint pass with 0 errors.

Verification

npm run lint
npx tsc --noEmit

Contributor Notes

Code clarity task. Do not alter any runtime function logic.

Start in src/lib/money.ts by reading dollarsToCents and formatCentsToCurrency and their existing comments. Add @param, @returns, and @example JSDoc blocks without changing runtime logic; examples should show integer-cent inputs and outputs. Run npm run lint and npx tsc --noEmit to verify the documentation changes.