Support selecting theme on the footer (#35741)

Fixes: https://github.com/go-gitea/gitea/pull/27576

web_src/svg/gitea-colorblind-redgreen.svg

@@ -0,0 +1,13 @@
+<svg width="40" height="40" viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <g clip-path="url(#clip0)">
+    <rect width="40" height="40" rx="20" fill="#0000"/>
+    <path d="M34.2843 34.2842C42.0948 26.4737 42.0948 13.8104 34.2843 5.9999L6 34.2842C13.8105 42.0947 26.4738 42.0947 34.2843 34.2842Z" fill="#0566D5"/>
+    <path d="M34.2828 34.2842C42.0932 26.4737 42.0932 13.8104 34.2828 5.99995L20.1406 20.1421L34.2828 34.2842Z" fill="#E7A100"/>
+    <circle cx="20" cy="20" r="18" fill="#0000" stroke="#aaa" stroke-width="4"/>
+  </g>
+  <defs>
+    <clipPath id="clip0">
+      <rect width="40" height="40" rx="20" fill="#0000"/>
+    </clipPath>
+  </defs>
+</svg>

web_src/svg/gitea-eclipse.svg

@@ -0,0 +1 @@
+<svg viewBox="490 490 820 820"><path d="M866.7 582.1A321.3 321.3 0 0 0 738.6 623a317.3 317.3 0 0 0-109.1 108.5A418 418 0 0 0 609 772a335.3 335.3 0 0 0-19.6 71.5 205.2 205.2 0 0 0-2.8 45c0 25.8.2 29.3 2.8 45 4.1 25.4 9.9 46.4 19.6 71.5a314.2 314.2 0 0 0 111.6 137.3A306.8 306.8 0 0 0 893 1196a308.6 308.6 0 0 0 303.6-262.5c2.6-15.7 2.8-19.2 2.8-45s-.2-29.3-2.8-45A335.3 335.3 0 0 0 1177 772a314.2 314.2 0 0 0-111.6-137.3A308.3 308.3 0 0 0 918 582c-13-1.1-38.2-1.1-51.3.1zM747 663.5l-2.4 16.7c-4 26.4-4.9 41.1-4.3 65.3a323.7 323.7 0 0 0 37.2 145c18.2 36 41.3 66.6 72 95.5a346.4 346.4 0 0 0 208.5 93.1l18 1.6 4.5.5-8.5 8a259.3 259.3 0 0 1-141.5 65.8 281 281 0 0 1-123.9-11.4 267.2 267.2 0 0 1-181.7-269.9c2-27.6 5.7-47.6 13.3-70.7a281.2 281.2 0 0 1 46.4-85c8-10.1 28-30.2 37.9-38.1 13.8-11.1 24.5-18.3 24.5-16.4z"/></svg>