feat: migrate to Vitest + doctest + TypeDoc, OIDC publishing, 5-platform CI

- Replace Jest with Vitest (native ESM/TS, no workarounds)
- Add vite-plugin-doctest for tested @example blocks in TSDoc
- Add TypeDoc for API reference generation
- Add TSDoc with doctest examples to presets, decode-options, errors
- Add TSDoc comments to all public API (client, pipeline, steps, io/*)
- Replace lazy require() with static imports in steps.ts
- Switch npm publish to OIDC trusted publishing with --provenance
- Expand CI matrix: ubuntu-24.04, macos-latest, macos-15-intel,
  windows-latest, windows-11-arm
- Add publish dry-run job to verify OIDC provenance in CI
- Update mozjpeg-sys 2.0.2 -> 2.2.3 (fixes Windows ARM NEON assembly)
- Remove Cargo.lock (rebuilt fresh each CI run)
- Add auto-update workflow for new imageflow releases
- Remove unnecessary LLVM/libclang CI steps
- Remove spell check workflow
- Bump actions: checkout v6, setup-node v6, cache v5
- Rewrite README for current ESM API with updated badges

110 tests (92 original + 18 doctest), all green on 5 platforms.

Author: lilith