feat: add channel enable/disable, prefab docs, and UI updates

Add per-channel enable/disable toggle to the in-game logging system
with Enable()/Disable() on InGameLogger and EnableChannel/DisableChannel
on IGameLogStore. Update README with prefab setup guide and enable/disable
documentation. Update character creation and log container prefabs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Packages/com.jovian.ingame-logging/Runtime/GameLogStore.cs

@@ -5,6 +5,7 @@ using UnityEngine;
 namespace Jovian.InGameLogging {
     public sealed class GameLogStore : IGameLogStore {
         readonly LogEntry[] buffer;
+        readonly HashSet<LogChannel> disabledChannels = new();
         int head;
         int count;
 
@@ -21,6 +22,9 @@ namespace Jovian.InGameLogging {
         }
 
         public void Add(LogChannel channel, string message) {
+            if(disabledChannels.Contains(channel)) {
+                return;
+            }
             var entry = new LogEntry(message, channel, Time.time);
             buffer[head] = entry;
             head = (head + 1) % buffer.Length;
@@ -30,6 +34,18 @@ namespace Jovian.InGameLogging {
             OnEntryAdded?.Invoke(entry);
         }
 
+        public void EnableChannel(LogChannel channel) {
+            disabledChannels.Remove(channel);
+        }
+
+        public void DisableChannel(LogChannel channel) {
+            disabledChannels.Add(channel);
+        }
+
+        public bool IsChannelEnabled(LogChannel channel) {
+            return !disabledChannels.Contains(channel);
+        }
+
         public void Clear() {
             head = 0;
             count = 0;