watch-help.js: image mirror non-recursive + one-shot at startup

[dnndev]

Problem

scripts/watch-help.js's deployImages() function had two shortcomings that left help images missing on the dev test site:

1. Non-recursive. The function iterated top-level files only with if (fs.statSync(src).isFile()), silently skipping any subdirectory. All v5 screenshots live in img/v5/, so every image referenced from a v5 doc page 404'd on xmp5dev.
2. One-shot at startup. Even when the watch is running, image changes during a session are not re-mirrored. Adding a new screenshot requires stopping and restarting the watcher.

Production packaging (Build-XmpV5.ps1 line 494) uses Copy-Item -Recurse so installed packages are unaffected — this is purely a local dev-deployment bug.

Status

• ✅ Recursion fix — landed in the same change that swapped the in-app help renderer to markdown-it. deployImages() now walks subdirectories with an inner mirrorDir() helper.
• ⏳ Watch-for-changes — still TODO. Either chokidar-watch the img/ tree alongside the markdown files, or accept one-shot and document a manual remirror command (e.g. npm run help:images).

Repro (pre-fix)

1. Add a screenshot to XModPro.Help/img/v5/
2. Run npm run help:watch
3. Observe: file is not copied to C:/TestSites/xmp5dev/DesktopModules/XModPro/help/img/v5/
4. Image 404s in the in-app help viewer

Suggested next step

Add a chokidar watcher for the img/ subtree that re-runs mirrorDir() (or a single-file copy) on add/change/unlink events. Debounce by file path the same way the markdown rebuild does.