chore(ui): drop AdminLTE 2, Bootstrap 3 and the rest of the dead front end

[mastacontrola]

FOG moved to AdminLTE 4 / Bootstrap 5 and the old bundles were never removed.

Nothing loaded them. Page declares every stylesheet and script in one
place (lib/fog/page.class.php, plus swagger on the API docs page), no plugin
declares its own assets, and the only references anywhere in the tree were
sourceMappingURL comments inside other minified files. So this was ~1.2 MB
of vendored code shipping in every release, sitting in every backup, and
answering "which bootstrap is this" with the wrong version.

It also actively misled: bootstrap5.min.css carries
sourceMappingURL=bootstrap.min.css.map, and the map of that name in the tree
was Bootstrap 3's — its sources begin less/normalize.less, the LESS
build BS3 used and BS5 does not. Devtools was resolving BS5 rules against BS3
sources.

Removed

	Files
AdminLTE 2	AdminLTE.min.css, adminlte-skins.min.css, adminlte.min.js
Bootstrap 3	bootstrap.min.css, its .map, bootstrap.min.js, css/less/ (71 LESS sources — there is no build step), and the glyphicons-halflings faces, which no loaded stylesheet has defined a rule for since the migration
Superseded	bootstrap-datetimepicker.min.{css,js} → js/fog/datetimepicker-shim.js re-implements $.fn.datetimepicker for the call sites still on the BS3-era API. jquery.color.min.js → shade() in fog.dashboard.js; the comment there already said so
Redundant	datatables.bootstrap5.min.{css,js} — datatables.min.css is a combined downloader build that already contains the Bootstrap 5 integration
Dead markup	the <!--[if lt IE 9]--> block in other/index.php, which is the shell for every page and pointed at dist/js/html5shiv.min.js and dist/js/respond.min.js — neither has ever existed in this tree, and Bootstrap 5 dropped IE outright

Tests

tests/retired-frontend-bundles.test.php, 23 checks, three mutation-verified:
a retired bundle reappearing, the datetimepicker shim being gutted, and
page.class.php starting to reference a retired file.

The replacements are checked by what they provide — $.fn.datetimepicker,
shade(), the --dt-row-selected rules — so gutting a file still fails,
rather than passing because the file happens to exist.

Verified live

Deployed to a 1.6 install (copybacktrunk rsyncs with --delete, so the
removals propagate) and then loaded in a browser:

• host list renders 86 rows and 144 sidebar links with zero failed
  resource requests
• every asset the login page references returns 200
• bootstrap5.min.css, adminlte4.min.css, datatables.min.css,
  font-awesome.min.css and the datetimepicker shim all still present and
  serving

Follow-up

Font Awesome is still 4.7.0. That is a separate change with a real blast
radius (the plugins repo uses fa fa-* too) and is being done next.

Downstream

None — no plugin references any removed file.