Scaffold the Rust and Node-API package architecture

[kylebernhardy]

Outcome

Create the production repository structure for the Rust engine, Node-API addon, generated bindings, TypeScript façade, native entry point, tests, examples, and platform packages, while reserving the Rocks entry point until its storage lease is proven.

Acceptance criteria

• Tantivy 0.26.1 and all native dependencies are pinned.
• Rust builds as both cdylib and rlib.
• The initial public import is @harperfast/fulltext/native; raw generated bindings are not public API.
• @harperfast/fulltext/rocks is added only after Phase 0 defines and tests the caller-owned rocksdb-js lease; the scaffold does not export a placeholder Rocks API.
• Native mode has no rocksdb-js dependency; Rocks mode will use an optional peer relationship.
• Apache-2.0 metadata, formatting, linting, unit-test commands, and contributor guidance are present.
• A native smoke test runs without Harper.

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