Add JSDoc/TSDoc descriptions for public APIs and enforce via lint rules

[sagpatil]

Motivation: Improve onboarding and in-editor discoverability by ensuring public functions and types have clear doc comments.

Proposed approach:

• Audit public API exports and add descriptive JSDoc/TSDoc for each function/type, with examples and parameter/return descriptions.
• Add lint rules or CI checks to require JSDoc on newly exported public APIs.

Acceptance criteria:

• Public API functions/types show hover docs in IDEs.
• CI/lint enforces doc presence for new public exports.

[sagpatil]

Parent epic: #1243