chore: stop tracking vendor lib files (now restored via npm + esbuild)

Drops 1038 files from src/Yavsc.Org/wwwroot/lib/ — they remain
on disk and are now restored via 'npm install' at build time
(see package.json and esbuild.config.mjs).

Exception: jonthornton-Datepair is not on npm, the bundled
files are kept in wwwroot/lib/jonthornton-Datepair/ as static
assets.

Also extends .gitignore to ignore:
- node_modules/, build/, package-lock.json (esbuild toolchain)
- wwwroot/js/*.min.js (regenerated by 'npm run build:js')
- .Production.env (added explicitly, not matched by '.*.env'
  glob in some git versions)

This aligns themeok with the architecture already in place
on refac/js-bundle (commits ed7522c5, 196f4b0b, 292c0a2f on
that branch). The build artifacts were already present in
node_modules/ and build/ on disk; this commit only stops
tracking them.

Tested: dotnet test 11/11 green (no C# code touched).

src/Yavsc.Org/wwwroot/lib/dropzone/basic.min.css

@@ -1 +0,0 @@
-.dropzone,.dropzone *{box-sizing:border-box}.dropzone{position:relative}.dropzone .dz-preview{position:relative;display:inline-block;width:120px;margin:.5em}.dropzone .dz-preview .dz-progress{display:block;height:15px;border:1px solid #aaa}.dropzone .dz-preview .dz-progress .dz-upload{display:block;height:100%;width:0;background:green}.dropzone .dz-preview .dz-error-message{color:red;display:none}.dropzone .dz-preview.dz-error .dz-error-mark,.dropzone .dz-preview.dz-error .dz-error-message{display:block}.dropzone .dz-preview.dz-success .dz-success-mark{display:block}.dropzone .dz-preview .dz-error-mark,.dropzone .dz-preview .dz-success-mark{position:absolute;display:none;left:30px;top:30px;width:54px;height:58px;left:50%;margin-left:-27px}