feat: add JEV-based PDF form-filling example

[bendersej]

Background

A public example showing Typesafe's JEV ("System One") model driving SimplePDF form-filling. It demonstrates the tenet code owns control flow, JEV answers narrow structured questions: the app orchestrates the editor via @simplepdf/react-embed-pdf actions, while JEV maps a CSV record onto fields, ticks checkboxes / picks constrained-field options, and judges plausibility. No agent, no hallucination.

Changes

• Next.js + Tailwind example under examples/with-typesafe, two forms (IRS W-9, Medication Prior Auth)
• JEV mapping (CSV column -> field) gated on calibrated confidence: auto-fill, confirm, or manual
• Constrained-field support: checkboxes and options driven off the field's own get_fields options
• JEV plausibility pass flags fictional / implausible values (e.g. a fake TIN)
• Human-in-the-loop: confirm low-confidence fills, a "Fill manually" path for red errors, live editor mirroring, and download
• Same-origin JEV proxy (/api/jev): path allowlist, redirect: "error", request timeout; BYOK key held in-memory only
• Benchmark harness (npm run bench): times JEV vs any OpenAI-compatible model on the same payload and reports output agreement, not just latency

Notes

The benchmark/ harness (and its vitest devDependency) is opt-in and self-contained. It needs NEXT_PUBLIC_TYPESAFE_API_KEY plus BENCHMARK_MODEL_BASE_URL / BENCHMARK_MODEL_ID / BENCHMARK_MODEL_API_KEY in .env.local to run the second model; delete the benchmark/ dir to ship the example JEV-only.