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.

templates/reader.templ

@@ -190,15 +190,16 @@ templ ReaderSettingsPanel() {
 					<h3 class="font-semibold">Reading Theme</h3>
 					<button
 						@click="toggleReadingMode()"
-						class="relative w-12 h-6 rounded-full transition-colors duration-200"
+						class="relative w-14 h-7 rounded-full transition-colors duration-200 flex items-center px-1"
 						:class="readingMode === 'dark' ? 'bg-blue-500' : 'bg-gray-400'"
 						type="button"
 						:aria-label="readingMode === 'dark' ? 'Switch to light mode' : 'Switch to dark mode'"
 					>
 						<span
-							class="absolute top-0.5 left-0.5 w-5 h-5 bg-white rounded-full shadow transition-transform duration-200"
-							:class="readingMode === 'dark' ? 'translate-x-6' : 'translate-x-0'"
-						></span>
+							class="absolute top-0.5 left-0.5 w-6 h-6 bg-white rounded-full shadow transition-transform duration-200 flex items-center justify-center text-xs"
+							:class="readingMode === 'dark' ? 'translate-x-7' : 'translate-x-0'"
+							x-text="readingMode === 'dark' ? '🌙' : '☀️'"
+						>☀️</span>
 					</button>
 				</div>
 				<label class="block mb-2">