Add .prettierignore for vendored minified JS (closes #185)

script/fmt ran prettier over static/js/*.js, which rewrote the vendored
minified static/js/alpine.min.js. A root .prettierignore with *.min.js
excludes vendored bundles: make fmt on a clean tree now yields no changes
and alpine.min.js stays byte-identical, while first-party JS still formats.

Model: opus-4-8

.prettierignore

@@ -0,0 +1,2 @@
+# Vendored, minified third-party bundles must never be reformatted.
+*.min.js

TODO.md

@@ -20,6 +20,8 @@ main cannot regress.
 
 # Completed Steps
 
+- 2026-09-22: Added `.prettierignore` so `make fmt` no longer rewrites
+  the vendored `static/js/alpine.min.js` bundle (#185).
 - 2026-09-09: Fixed four deployability blockers found by QA: CSRF origin
   check over plain HTTP (`UPAAS_PLAINTEXT_HTTP`, #189), pulling the git
   image when absent (#190), the env-var editor CSRF token lookup (#191),