Update CLAUDE.md and ARCHITECTURE.md for Behavior/Archetype redesign and editor mode

Documents the replacement of Element with Behavior + Archetype, the
elimination of the per-board element palette, the new map file format
(archetype = "name" instead of passable = bool), the ErrorBlock sentinel,
and the editor mode (AppMode, EditorState, palette panel, click-to-paint).
Also updates "What's not yet implemented" to reflect editor progress and
call out the Object behavior / glyph chooser / file open gaps.

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

src/main.rs

@@ -221,4 +221,4 @@ fn draw_glyph(painter: &egui::Painter, origin: Pos2, x: usize, y: usize, glyph:
     let center = rect.center();
     painter.rect_filled(rect, 0.0, glyph.bg);
     painter.text(center, Align2::CENTER_CENTER, glyph.ch, FontId::monospace(CELL_H), glyph.fg);
-}
+}