fix(ruvector): Node 22 LTS-compatible ONNX WASM loader (#323)

[ruvnet]

Summary

• Closes ONNX embedder fails on Node 22 LTS with 'Unknown file extension .wasm' #323 — initOnnxEmbedder() failed on Node 22 LTS with Error: Unknown file extension ".wasm" because the bundled pkg/ruvector_onnx_embeddings_wasm.js is wasm-bindgen's --target bundler output and starts with import * as wasm from "./ruvector_onnx_embeddings_wasm_bg.wasm";. Node 22 rejects static .wasm imports without --experimental-wasm-modules; Node 25+ accepts them natively, which masked the regression.

Fix

• Add src/core/onnx/pkg/ruvector_onnx_embeddings_wasm_node.mjs: Node-friendly sibling entry that uses fs.readFileSync + WebAssembly.compile/instantiate, with the host imports routed through the existing _bg.js.
  • Import-module name (./ruvector_onnx_embeddings_wasm_bg.js) verified by inspecting the WASM binary's import section.
  • Calls instance.exports.__wbindgen_start() if present (mirrors the bundler-target glue).
• onnx-embedder.ts now prefers the new _node.mjs entry when present and falls back to the bundler entry — so existing installs without the new file aren't broken by this change.
• The bundler-target file is untouched, so webpack/vite/rollup consumers keep working.
• Add test/onnx-node22-loader.test.mjs regression guard.

Proof

On Node v22.22.2 (without --experimental-wasm-modules):

$ node test/onnx-node22-loader.test.mjs
Node version: v22.22.2
  ok: Node-friendly loader exists in src/core/onnx/pkg/
  ok: loader produced a module namespace
  ok: re-exports __wbg_set_wasm
  ok: re-exports WasmEmbedder
  ok: re-exports WasmEmbedderConfig

Node v22.22.2 ONNX loader smoke OK

$ npx tsc --noEmit
# (no errors)

Test plan

• Loader imports cleanly on Node 22 LTS (no Unknown file extension ".wasm").
• Re-exports the wasm-bindgen surface (__wbg_set_wasm, WasmEmbedder, WasmEmbedderConfig).
• Project type-checks (tsc --noEmit).
• onnx-embedder.ts falls back gracefully when _node.mjs is absent (older bundles still load).
• Manual: clean install → initOnnxEmbedder() → embed text on Node 22 LTS. Requires ONNX WASM files not bundled on clean insteall #354/CLI commands that take a <database> path are broken on freshly-created DBs (and embed text fails on missing ONNX bundle) #417 bundling fix to land for the dist/ path to be populated.

Scope notes

• End-to-end fresh-install of initOnnxEmbedder() also requires the build script to copy src/core/onnx/pkg/ → dist/core/onnx/pkg/ — tracked separately as ONNX WASM files not bundled on clean insteall #354 and CLI commands that take a <database> path are broken on freshly-created DBs (and embed text fails on missing ONNX bundle) #417. This PR is the loader fix only; once ONNX WASM files not bundled on clean insteall #354/CLI commands that take a <database> path are broken on freshly-created DBs (and embed text fails on missing ONNX bundle) #417 land, the loader change here makes the path work on all supported Node versions.
• No version bump in this PR — release pipeline owns versioning.

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