[2f] Add TypeScript declarations, JSDoc, and fix nftMarkerCount/markerNFTCount naming

Start by inventorying the public methods in src/ARFset.js and related source files, then inspect examples for uses of nftMarkerCount and markerNFTCount. Done means the public API has TypeScript declarations, JSDoc with parameter and return information, and one consistent marker-count name throughout src/ and examples.

Summary

Add TypeScript declarations, JSDoc on all public methods, and resolve nftMarkerCount / markerNFTCount naming inconsistency

Environment

• Product/Service: FeatureSET-Display — JavaScript API
• Files: src/ARFset.js and related source files

Problem Description

Three related API-quality gaps:

1. No type declarations: No .d.ts file exists, so TypeScript consumers get no type checking or IDE autocompletion.
2. No JSDoc: Public methods have no documentation, making the API opaque to new consumers.
3. Naming inconsistency: nftMarkerCount (field name) and markerNFTCount (local variable name) diverge — one of them is wrong, and the inconsistency is a footgun for callers.

Expected Behavior

• A .d.ts declaration file (or TypeScript source) covers all public API surface.
• Every public method has a JSDoc comment with parameter types, return type, and a one-line description.
• nftMarkerCount / markerNFTCount are reconciled to a single consistent name throughout the codebase.

Actual Behavior

No type declarations, no JSDoc, inconsistent public naming.

Tasks

• Add TypeScript declarations (.d.ts) — or convert src/ to TypeScript outright
• Add JSDoc on every public method
• Decide on naming: nftMarkerCount vs markerNFTCount and rename consistently throughout src/ and any examples

Impact

Low — Developer experience and API usability. No runtime behavior change.

Additional Context

Converting src/ to TypeScript directly is the higher-value option (catches bugs at compile time, generates .d.ts automatically) but is a larger scope. Adding a hand-authored .d.ts is a quick win that unblocks TypeScript consumers immediately. The naming fix should happen regardless of which approach is chosen.