wasm: first-class JavaScript/TypeScript embedding surface

[Fieldnote-Echo]

Summary

Design a first-class JavaScript/TypeScript WASM embedding surface for ordvec.

This is an ecosystem compatibility issue. The core crate already targets wasm32, but browser and Node users need a clear package/API contract. ordvec should expose scoring primitives without owning application storage, metadata, or database lifecycle.

Proposed scope

Create a design and initial package plan for an ordvec-wasm surface, likely with wasm-bindgen or equivalent. Start with read-only primitives:

• load/probe persisted RankQuant, Bitmap, and SignBitmap where practical
• Float32Array query inputs
• Uint32Array candidate/docset inputs
• full search and subset rerank
• explicit free()/lifetime rules
• TypeScript declarations
• Worker/browser/Node examples

Index building can be staged later and should align with Rust/C builder work.

Acceptance criteria

• Design doc states package name, supported runtimes, memory/lifetime model, and API shape.
• Node and headless-browser smoke tests run a fixture search.
• TypeScript declarations ship with the package when implemented.
• Docs make clear that storage, metadata, filters, and sync remain host responsibilities.
• Uses runtime feature guidance for wasm SIMD where relevant.

Non-goals

• No browser vector database.
• No IndexedDB/OPFS storage layer by default.
• No app framework or hosted service.