Remove webinterface settings tab and configuration fields

Webinterface adds a third-party HTTP surface that contradicts the
DSGVO-by-default promise: it broadcasts every chat message including
filtered ChatTypes (privacy filter only covers DB writes), ships a
five-digit numeric auth code seeded from System.Random, binds on all
interfaces by default and sets cookies without security flags.

Hardening it for our threat model would land 500+ lines of code and
permanent maintenance for a feature very few users actually use. The
forks audience wants less surface, not more, so the entire feature is
being removed in a focused commit cluster. This first commit drops
the user-facing surface: settings tab class, tab registration and
the Configuration fields plus their UpdateFrom mirror.

ChatTwo/Configuration.cs

@@ -171,14 +171,6 @@ public class Configuration : IPluginConfiguration
     public ConfigKeyBind? ChatTabForward;
     public ConfigKeyBind? ChatTabBackward;
 
-    // Webinterface
-    public bool WebinterfaceEnabled;
-    public bool WebinterfaceAutoStart;
-    public string WebinterfacePassword = WebinterfaceUtil.GenerateSimpleAuthCode();
-    public int WebinterfacePort = 9000;
-    public HashSet<string> AuthStore = [];
-    public int WebinterfaceMaxLinesToSend = 1000; // 1-10000
-
     public void UpdateFrom(Configuration other, bool backToOriginal)
     {
         if (backToOriginal)
@@ -243,11 +235,6 @@ public class Configuration : IPluginConfiguration
         ChosenStyle = other.ChosenStyle;
         ChatTabForward = other.ChatTabForward;
         ChatTabBackward = other.ChatTabBackward;
-        WebinterfaceEnabled = other.WebinterfaceEnabled;
-        WebinterfaceAutoStart = other.WebinterfaceAutoStart;
-        WebinterfacePassword = other.WebinterfacePassword;
-        WebinterfacePort = other.WebinterfacePort;
-        WebinterfaceMaxLinesToSend = other.WebinterfaceMaxLinesToSend;
 
         PrivacyFilterEnabled = other.PrivacyFilterEnabled;
         PrivacyPersistChannels = [..other.PrivacyPersistChannels];