Properties: open a dropdown only on the surface that asked (#1766)

The docked panel and Quick Properties render the same rows from one
state, so a picked colour opened both dropdowns and each swallowed the
other's click.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/mod.rs

@@ -3625,6 +3625,8 @@ pub enum Message {
     PropPointerPressed,
     /// Toggle the inline color picker dropdown open/closed.
     PropColorPickerToggle,
+    /// A Properties dropdown toggle and whether Quick Properties sent it.
+    PropPickerSurface(bool, Box<Message>),
     /// Toggle the MTEXT background-colour picker dropdown open/closed.
     PropBgColorPickerToggle,
     /// User picked an MTEXT background fill colour — sets `background_color`