feat: iOS appearance, iPad logo fix, demo seed, and landing hero polish

Add System/Light/Dark preference for iPhone and iPad, restore the iPad
sidebar brand mark, ship a DEBUG seed-demo URL for rich placeholder data,
and refresh GitHub Pages with the device composite, full-bleed pale-green
hero wash, and transparent Mac screenshot chrome.

OSGKeyboardMac/Info.plist

@@ -23,6 +23,17 @@
 	<string>APPL</string>
 	<key>CFBundleShortVersionString</key>
 	<string>$(MARKETING_VERSION)</string>
+	<key>CFBundleURLTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleURLName</key>
+			<string>com.osgkeyboard.mac.seed</string>
+			<key>CFBundleURLSchemes</key>
+			<array>
+				<string>osgkeyboard</string>
+			</array>
+		</dict>
+	</array>
 	<key>CFBundleVersion</key>
 	<string>$(CURRENT_PROJECT_VERSION)</string>
 	<key>ITSAppUsesNonExemptEncryption</key>