Add Javstash Autofill plugin

[suzuhiroruri]

What this adds

plugins/javstashAutofill — a Performer.Create.Post hook that fills a newly-created performer's empty fields from a scraper (default: the javstash stash-box), using the best name-matching candidate (or skipping when there is no match).

Features

• Best name match, or skip (configurable threshold).
• Fill empty only by default — existing values, images and aliases are protected. Every field has an optional per-field overwrite toggle.
• Primary-name policy per origin (Identify vs. manual, detected via stash_ids in the create input): keep the created name (scraper name → alias) or make the scraper's canonical name primary (created name → alias).
• Duplicate merge: when the scraper name would become primary but a same-named performer already exists, the new one is merged into it via performerMerge (scenes re-linked, created name kept as alias, stash-box id carried over).
• Measurements normalisation (91H-56-88 → 91(H)-56-88).
• Asynchronous image — the image is fetched and set in a detached process so the hook returns immediately and Stash never blocks on a slow remote image fetch.

Configurable source (stash-box endpoint or scraper_id), separately for Identify and manual creation. Standard library only.

Validation

• node ./validate.js --ci — Validation passed.
• Manually tested on a live Stash (native macOS build) against the javstash stash-box: empty-fill, per-field overwrite, keep-created-name vs. use-scraper-name for both origins, duplicate merge (stash_id + aliases carried over), and asynchronous image setting. Test performers were removed afterwards.

LLM-assisted contribution disclosure

Per the repository's LLM policy: this plugin was written with LLM assistance (Claude). The code was human-reviewed and human-tested/validated on a live instance, and I take full responsibility for it (including license compliance).