feat(ui): add separate icon and text colorization for CustomButton

- Add colorizeSystemText setting for text color (icon only was already supported)
- JSON parse supports iconColor and textColor fields separately
- Legacy "color" field still works for both icon and text
- Enable colorization no longer depends on show icon setting
- Refactor resolveColor helper to eliminate duplicate code

Assets/Translations/en.json

@@ -105,6 +105,8 @@
       "collapse-condition-description": "If the output text matches this value, the button will collapse.",
       "collapse-condition-label": "Collapse condition",
       "color-selection-description": "Apply theme colors to icon and text.",
+      "icon-color-selection-description": "Apply theme colors to icons.",
+      "text-color-selection-description": "Apply theme colors to text.",
       "default-tooltip": "Custom button, configure in settings",
       "display-command-output-description": "Enter a command to run at a regular interval. The first line of its output will be displayed as text.",
       "display-command-output-label": "Display command output",
@@ -523,6 +525,7 @@
     "select-color": "Select color",
     "select-color-description": "Apply theme colors for emphasis.",
     "select-icon-color": "Select icon color",
+    "select-text-color": "Select text color",
     "settings": "Settings",
     "shortcuts": "Shortcuts",
     "shutdown": "Shutdown",