Remove dead CSS (#37376)

Removes CSS rules that have zero usages across templates, Go source,
JS/TS/Vue, and `options/`. Each selector was cross-checked for runtime
additions (Fomantic JS, library classes) before removal.

A few rules with no current usages are kept as symmetric pairs of
heavily-used classes likely to be needed:
- `.ui.bottom.attached.header` / `.ui.bottom.attached.message` — pair
with the widely-used `top.attached` variants
- `.ui.warning.header` / `.ui.warning.segment` — warning-themed variants
of error-themed classes that are kept
- `.btn.small` — size variant alongside the kept `.btn.tiny`

---
This PR was written with the help of Claude Opus 4.7

---------

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

web_src/css/modules/comment.css

@@ -32,23 +32,6 @@
   padding-top: 0;
 }
 
-.ui.comments .comment > .comments {
-  margin: 0 0 0.5em 0.5em;
-  padding: 1em 0 1em 1em;
-}
-
-.ui.comments .comment > .comments::before {
-  position: absolute;
-  top: 0;
-  left: 0;
-}
-
-.ui.comments .comment > .comments .comment {
-  border: none;
-  border-top: none;
-  background: none;
-}
-
 .ui.comments .comment > .content {
   display: flex;
   flex-direction: column;
@@ -56,21 +39,6 @@
   min-width: 0;
 }
 
-.ui.comments .comment .metadata {
-  display: inline-block;
-  margin-left: 0.5em;
-  font-size: 0.875em;
-}
-
-.ui.comments .comment .metadata > * {
-  display: inline-block;
-  margin: 0 0.5em 0 0;
-}
-
-.ui.comments .comment .metadata > :last-child {
-  margin-right: 0;
-}
-
 .ui.comments .comment .text {
   margin: 0.25em 0 0.5em;
   font-size: 1em;