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/input.css

@@ -69,42 +69,24 @@
   visibility: hidden;
 }
 
-.ui.ui.ui.ui.icon.input > textarea,
 .ui.ui.ui.ui.icon.input > input {
   padding-right: 2.67142857em;
 }
-.ui.icon.input > i.link.icon {
-  cursor: pointer;
-}
-.ui.icon.input > i.circular.icon {
-  top: 0.35em;
-  right: 0.5em;
-}
 
 .ui[class*="left icon"].input > i.icon {
   right: auto;
   left: 1px;
   border-radius: 0.28571429rem 0 0 0.28571429rem;
 }
-.ui[class*="left icon"].input > i.circular.icon {
-  right: auto;
-  left: 0.5em;
-}
-.ui.ui.ui.ui[class*="left icon"].input > textarea,
 .ui.ui.ui.ui[class*="left icon"].input > input {
   padding-left: 2.67142857em;
   padding-right: 1em;
 }
 
-.ui.icon.input > textarea:focus ~ .icon,
 .ui.icon.input > input:focus ~ .icon {
   opacity: 1;
 }
 
-.ui.icon.input > textarea ~ i.icon {
-  height: 3em;
-}
-
 .ui.form .field.error > .ui.action.input > .ui.button,
 .ui.action.input.error > .ui.button {
   border-top: 1px solid var(--color-error-border);