ios: full feature/appearance parity with the macOS app (client-side)

Port the Mac's MarkdownText renderer, AppPalette (color-vision modes +
night-softening), appearance settings (theme/text size/color vision),
and BuildBanner channel strip to the iPhone remote. Add session-row
attention/unseen-completion washes and marker icons, Discard action,
branch/worktree options in the new-chat composer, and a transient
error bubble for host wire errors. Stamp the build channel via
NucleicChannel in Info.plist (ios-release.sh passes NUCLEIC_CHANNEL,
default beta). Demo mode gains NUCLEIC_DEMO_SESSION and skips the
notifications prompt so UI previews are scriptable.

Co-Authored-By: Claude Fable 5 <[email protected]>

NucleicRemote/NucleicRemote/Info.plist

@@ -6,5 +6,7 @@
 	<array>
 		<string>_nucleic._tcp</string>
 	</array>
+	<key>NucleicChannel</key>
+	<string>$(NUCLEIC_CHANNEL)</string>
 </dict>
 </plist>