[enh] theme/simple: custom router

Lay the foundation for loading scripts granularly depending on the endpoint it's
on.

Remove vendor specific prefixes as there are now managed by browserslist and
LightningCSS.

Enabled quite a few rules in Biome that don't come in recommended to better
catch issues and improve consistency.

Related:

- https://github.com/searxng/searxng/pull/5073#discussion_r2256037965
- https://github.com/searxng/searxng/pull/5073#discussion_r2256057100

client/simple/src/less/code.less

@@ -18,11 +18,7 @@
       cursor: default;
 
       &::selection {
-        background: transparent; /* WebKit/Blink Browsers */
-      }
-
-      &::-moz-selection {
-        background: transparent; /* Gecko Browsers */
+        background: transparent;
       }
 
       margin-right: 8px;

client/simple/src/less/mixins.less

@@ -2,9 +2,6 @@
 
 // Mixins
 .text-size-adjust (@property: 100%) {
-  -webkit-text-size-adjust: @property;
-  -ms-text-size-adjust: @property;
-  -moz-text-size-adjust: @property;
   text-size-adjust: @property;
 }
 
@@ -22,7 +19,6 @@
 
 // disable user selection
 .disable-user-select () {
-  -webkit-touch-callout: none;
   user-select: none;
 }
 

client/simple/src/less/rss.less

@@ -1,12 +1,6 @@
 @import (inline) "../../node_modules/normalize.css/normalize.css";
 @import "definitions.less";
-
-.text-size-adjust (@property: 100%) {
-  -webkit-text-size-adjust: @property;
-  -ms-text-size-adjust: @property;
-  -moz-text-size-adjust: @property;
-  text-size-adjust: @property;
-}
+@import "mixins.less";
 
 // Reset padding and margin
 html,

client/simple/src/less/search.less

@@ -196,11 +196,6 @@ html.no-js #clear_search.hide_if_nojs {
   .ltr-rounded-left-corners(0.8rem);
 }
 
-#q::-ms-clear,
-#q::-webkit-search-cancel-button {
-  display: none;
-}
-
 #send_search {
   .ltr-rounded-right-corners(0.8rem);
 
@@ -271,7 +266,6 @@ html.no-js #clear_search.hide_if_nojs {
       width: 100%;
       .ltr-text-align-left();
       overflow: scroll hidden;
-      -webkit-overflow-scrolling: touch;
     }
   }
 }
@@ -374,11 +368,6 @@ html.no-js #clear_search.hide_if_nojs {
 
 #categories {
   .disable-user-select;
-
-  &::-webkit-scrollbar {
-    width: 0;
-    height: 0;
-  }
 }
 
 #categories_container {

client/simple/src/less/style-rtl.less

@@ -129,13 +129,7 @@
 }
 
 // select HTML element
-@supports (
-  (background-position-x: 100%) and
-    (
-      (appearance: none) or (-webkit-appearance: none) or
-        (-moz-appearance: none)
-    )
-) {
+@supports ((background-position-x: 100%) and ((appearance: none))) {
   select {
     border-width: 0 0 0 2rem;
     background-position-x: -2rem;

client/simple/src/less/toolkit.less

@@ -156,9 +156,7 @@ div.selectable_url {
 
   td {
     padding: 0 1em 0 0;
-    padding-top: 0;
     .ltr-padding-right(1rem);
-    padding-bottom: 0;
     .ltr-padding-left(0);
   }
 
@@ -307,7 +305,7 @@ html body .tabs > input:checked {
   }
 
   ~ label {
-    position: inherited;
+    position: inherit;
     background: inherit;
     border-bottom: 2px solid transparent;
     font-weight: normal;
@@ -347,17 +345,9 @@ select {
   }
 }
 
-@supports (
-  (background-position-x: 100%) and
-    (
-      (appearance: none) or (-webkit-appearance: none) or
-        (-moz-appearance: none)
-    )
-) {
+@supports ((background-position-x: 100%) and ((appearance: none))) {
   select {
     appearance: none;
-    -webkit-appearance: none;
-    -moz-appearance: none;
     border-width: 0 2rem 0 0;
     border-color: transparent;
     background: data-uri("image/svg+xml;charset=UTF-8", @select-light-svg-path)
@@ -400,8 +390,6 @@ select {
 
 /* -- checkbox-onoff -- */
 input.checkbox-onoff[type="checkbox"] {
-  -webkit-appearance: none;
-  -moz-appearance: none;
   appearance: none;
   cursor: pointer;
   display: inline-block;
@@ -475,8 +463,6 @@ input.checkbox-onoff.reversed-checkbox[type="checkbox"] {
 /* -- checkbox -- */
 @supports (transform: rotate(-45deg)) {
   input[type="checkbox"]:not(.checkbox-onoff) {
-    -webkit-appearance: none;
-    -moz-appearance: none;
     appearance: none;
 
     width: 20px;
@@ -549,33 +535,16 @@ input.checkbox-onoff.reversed-checkbox[type="checkbox"] {
   border-right: 0.5em solid var(--color-toolkit-loader-border);
   border-bottom: 0.5em solid var(--color-toolkit-loader-border);
   border-left: 0.5em solid var(--color-toolkit-loader-borderleft);
-  -webkit-transform: translateZ(0);
-  -ms-transform: translateZ(0);
   transform: translateZ(0);
-  -webkit-animation: load8 1.2s infinite linear;
   animation: load8 1.2s infinite linear;
 }
 
-@-webkit-keyframes load8 {
-  0% {
-    -webkit-transform: rotate(0deg);
-    transform: rotate(0deg);
-  }
-
-  100% {
-    -webkit-transform: rotate(360deg);
-    transform: rotate(360deg);
-  }
-}
-
 @keyframes load8 {
   0% {
-    -webkit-transform: rotate(0deg);
     transform: rotate(0deg);
   }
 
   100% {
-    -webkit-transform: rotate(360deg);
     transform: rotate(360deg);
   }
 }
@@ -606,9 +575,6 @@ td:hover .engine-tooltip,
   margin: 0;
   padding: 0 0.125rem 0 4rem;
   width: 100%;
-  width: -moz-available;
-  width: -webkit-fill-available;
-  width: fill;
   flex-flow: row nowrap;
   align-items: center;
   display: inline-flex;