ShareLinks: keep player back button, disable in-item links, hide add-to-playlist, generalize guest plugin hiding

Hiding .headerBackButton for guests also removed the video player's back
button (same class), so a guest could not return from playback to the
movie page. Stop hiding that class; keep home/drawer/search hidden.

Cast, studio, genre and tag links on the detail page now have
pointer-events disabled for guests so they stay visible but inert
(clicking Studio no longer spins on a page the guest cannot load), and
the add-to-playlist/add-to-collection actions are hidden.

Add a GuestHiddenSelectors config field (comma-separated CSS selectors,
surfaced through GuestState since guests cannot read plugin config) so
other plugins injected UI can be suppressed for guest sessions without
code changes; defaults to hiding the AI Search elements.

Jellyfin.Plugin.ShareLinks/Configuration/PluginConfiguration.cs

@@ -41,4 +41,12 @@ public class PluginConfiguration : BasePluginConfiguration
 
     /// <summary>Gets or sets a value indicating whether guest-mode lockdown is enabled.</summary>
     public bool GuestModeLockdownEnabled { get; set; } = true;
+
+    /// <summary>
+    /// Gets or sets a comma-separated list of CSS selectors that are hidden from guest
+    /// sessions in the web client. Used to suppress other plugins' injected UI (search
+    /// bars, floating buttons) so a guest only sees the shared title. Defaults to the
+    /// AI Search plugin's elements.
+    /// </summary>
+    public string GuestHiddenSelectors { get; set; } = ".ais-fab,.ais-overlay,#ais-styles";
 }