agent links: revert screen's VS16 — renders as a stray char for mara

The variation selector was meant to force emoji presentation, but her
font renders it as a separate unrenderable glyph instead of being
silently consumed. Screen's bare codepoint was already a real emoji
before this PR touched it — didn't need changing at all.

hive-agent/src/web_ui/state.rs

@@ -324,7 +324,7 @@ fn agent_links(label: &str, gui_enabled: bool) -> Vec<AgentLink> {
     if gui_enabled {
         links.push(AgentLink {
             url: "screen.html".to_owned(),
-            icon: "🖥️".to_owned(),
+            icon: "🖥".to_owned(),
             label: "screen".to_owned(),
             kind: AgentLinkKind::Container,
         });