[PowerDisplay] Add custom vcp code name map and fix some bugs (#45355)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
1. Fix quick access not working bug
2. Add custom value mapping
3. Fix some vcp slider visibility bug

demo for custom vcp value name mapping:
<img width="1399" height="744" alt="image"
src="https://github.com/user-attachments/assets/517e4dbb-409a-4e43-b15a-d0d31e59ce49"
/>
<img width="1379" height="337" alt="image"
src="https://github.com/user-attachments/assets/18f6f389-089c-4441-ad9f-5c45cac53814"
/>
<img width="521" height="1152" alt="image"
src="https://github.com/user-attachments/assets/27b5f796-66fa-4781-b16f-4770bebf3504"
/>
<img width="295" height="808" alt="image"
src="https://github.com/user-attachments/assets/54eaf5b9-5d54-4531-a40b-de3113122715"
/>


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Co-authored-by: Yu Leng <yuleng@microsoft.com>

src/settings-ui/Settings.UI.Library/PowerDisplayProperties.cs

@@ -23,6 +23,7 @@ namespace Microsoft.PowerToys.Settings.UI.Library
             ShowSystemTrayIcon = true;
             ShowProfileSwitcher = true;
             ShowIdentifyMonitorsButton = true;
+            CustomVcpMappings = new List<CustomVcpValueMapping>();
 
             // Note: saved_monitor_settings has been moved to monitor_state.json
             // which is managed separately by PowerDisplay app
@@ -61,5 +62,12 @@ namespace Microsoft.PowerToys.Settings.UI.Library
         /// </summary>
         [JsonPropertyName("show_identify_monitors_button")]
         public bool ShowIdentifyMonitorsButton { get; set; }
+
+        /// <summary>
+        /// Gets or sets custom VCP value name mappings shared across all monitors.
+        /// Allows users to define custom names for color temperature presets and input sources.
+        /// </summary>
+        [JsonPropertyName("custom_vcp_mappings")]
+        public List<CustomVcpValueMapping> CustomVcpMappings { get; set; }
     }
 }