fix(reader): use blob URLs for fonts to bypass sandboxed iframe restrictions

The paginator renders inside a sandboxed iframe that blocks @font-face
URL fetches. Fonts were never loading — all font-family rules fell back
to the generic 'serif' system font, making every reading font identical.

Fix: fetch font files on the parent page, create blob: URLs via
URL.createObjectURL(), and use those blob URLs in the @font-face rules
injected into the iframe via setStyles(). Blob URLs are always
same-origin with the creating document, so the sandboxed iframe can
access them with allow-same-origin.

Also added Playwrite NZ Guides as a test font for verifying font
switching works.

templates/reader.templ

@@ -258,6 +258,7 @@ templ ReaderSettingsPanel() {
 						<option value="noto-serif">Noto Serif</option>
 						<option value="charis-sil">Charis SIL</option>
 						<option value="ibm-plex">IBM Plex Serif</option>
+						<option value="playwrite">Playwrite NZ Guides (Test)</option>
 					</select>
 				</label>
 				<label class="block mb-2">