Frontend: LiteSpeed's minifier cuts a regex in half and stops every combined script for visitors #2056

Problem

On the testing site, the verification page's device test (/valid/?ffc_device_check=1) stays at "Checking…" on every row for visitors who are not logged in, on phones and on desktop. A logged-in administrator sees it work.

Cause

LiteSpeed Cache minifies and combines scripts for guests. Its minifier, matthiasmullie/minify, mishandles a regex literal that ends in an escaped slash. When the literal is followed by ] or a line break, the minifier treats the closing slash as the start of a comment and drops the rest of the line. The rendered output on the testing site shows it:

• source: ['LINE', /Line\//]
• minified: ['LINE',/Line\];var BRANDS=…

The combined file then fails to parse ("Invalid regular expression: missing /"), so no script in it runs. The literal came in with #2053. Two more literals of the same shape exist (ffc-core.js, ffc-preflight.js); their current neighbours happen to survive minification.

Acceptance criteria

• No regex literal in assets/js/ ends in an escaped slash. The three existing ones are rewritten to \/\d or \/{2}.
• Every readable script in assets/js/ and libs/js/ runs through matthiasmullie/minify and still parses (verified once, by hand).
• A guard test refuses the shape, with a canary and an independent recount of the scanned files.
• CHANGELOG entry under Fixed.