Add glyph chooser and redesign editor side panel

Glyph chooser: a painted preview button in the Palette tab opens a
floating dialog with a board-palette picker, fg/bg color pickers
(egui built-in), and a 16×6 printable ASCII character grid. The
stamped glyph is now independent of the archetype's default.

Side panel: widened to 200 px (resizable), tabbed (Palette / Board /
World), archetype rows show their default glyph cell, list scrolls
after 5 entries, labels use ui.label() for consistent sizing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/game.rs

@@ -12,7 +12,7 @@ use serde::Deserialize;
 /// `Glyph` values come from the map file palette and are set at load time.
 /// The player is the only entity whose glyph is hardcoded at runtime
 /// (see [`Glyph::player`]).
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, PartialEq)]
 pub struct Glyph {
     /// The character to display in this cell.
     pub ch: char,