feat(ml): IMF v1 runtime — index resolution, sha256 verification, KV decode (WO05)

[ronaldtse]

Summary

The TypeScript binding of interscript-ml (WO05): an IMF v1 runtime
under src/ml/imf/, implementing the models.yaml contract shared with
the Python reference (interscript-ml) and the Ruby binding (secryst
PR #45). Stacked on #5; retarget when it merges.

What's here

• tokens — the canonical ByT5 table (byte b → id b+3, trailing
  EOS). Ids are NOT raw TextEncoder bytes.
• loader — fflate unzip + js-yaml manifest; every .onnx member
  sha256-verified via WebCrypto before any session is created.
• registry — models.yaml resolution: verified cache hit in
  ~/.cache/interscript/models/<id>/ (node fs, atomic rename), or
  download → whole-file sha256 verify. Env overrides match the other
  runtimes (INTERSCRIPT_ML_INDEX, INTERSCRIPT_ML_CACHE).
• IMFModel — greedy KV-cache decode when the zip ships
  decoder-kv.onnx (default), plain full-recompute fallback;
  zero-length step-0 pasts sized from session inputMetadata (now
  exposed through the node session wrapper — additive interface change).
• deps: fflate, js-yaml (+types), onnxruntime-node as devDep.

Cross-runtime acceptance

Released khm-latn-1.0 (interscript/ml-models): 100/100 golden-set
outputs byte-identical across TypeScript, Python, and Ruby —
golden/khm-latn-100.jsonl is the shared contract.

Test plan

• vitest: 8 tests (token table, manifest + tamper rejection,
  registry install/cache-hit/unknown-id, session loading from the
  committed tiny IMF fixture, golden e2e gated on
  INTERSCRIPT_TS_E2E_ZIP)
• golden e2e against the released zip: 8/8
• tsc clean (exactOptionalPropertyTypes honored); full suite
  241 tests green
• CI

Note: package-lock.json carries the base branch's pre-existing
in-flight dependency state alongside the two new deps.

[ronaldtse]

CI note: Build+Test and Coverage fail on this PR, but they fail
identically on the base PR #5 (unused-vars lint and coverage thresholds
in the base's committed state — the in-flight working tree appears to
address them). This branch's own changes lint clean (eslint src/ml/imf test/imf.test.ts → no findings), tsc is clean under
exactOptionalPropertyTypes, and the full suite passes locally: 241
tests, 8/8 IMF including the 100/100 golden e2e against the released
khm-latn-1.0. Happy to rebase once #5 lands.