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

script/fmt passes the glob static/js/*.js to prettier, which expanded
and rewrote the vendored static/js/alpine.min.js because there was no
ignore file. Add .prettierignore excluding *.min.js; prettier honors it
even when files are passed explicitly on the command line, so make fmt
now leaves the tree byte-identical while still formatting first-party
JS.

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),