fix(reader): dark text on dark themes and add toggle icons

Two fixes:

1. Remove base typography block from foliate-themes.css. The html/body
   rules were unlayered CSS that overrode the chrome theme's layered
   body styles, causing dark reading theme text colors (--reader-text)
   to apply to the outer chrome UI on dark backgrounds. These styles
   are only meant for the shadow DOM, which getCSS() already handles.

2. Move missing typography rules (img, blockquote, a, p orphans/widows)
   into getCSS() so the shadow DOM still gets them.

3. Add sun/moon emoji indicators to the light/dark toggle switch.

web/src/reader/reader.ts

@@ -59,6 +59,26 @@ const getCSS = ({
     aside[epub|type~="rearnote"] {
         display: none;
     }
+    img, svg, video {
+        max-width: 100%;
+        height: auto;
+        display: block;
+        margin: 0.5em auto;
+    }
+    p {
+        orphans: 3;
+        widows: 3;
+    }
+    blockquote {
+        margin: 1em 0;
+        padding-left: 1em;
+        border-left: 3px solid ${link};
+        font-style: italic;
+    }
+    a {
+        color: ${link};
+        text-decoration: underline;
+    }
 `;
 };
 document.addEventListener("alpine:init", () => {