Object passable/opaque: editor checkboxes + doc/simplify cleanup

- ObjectDef gains passable/opaque fields (defaults: false/true); Board::is_passable
  consults the object before the grid cell, so objects block movement independently
  of the floor tile beneath them
- Editor Objects tab exposes Passable and Opaque checkboxes; changes survive save/load
- Add ObjectDef::new(x, y) to centralise placement defaults; remove triple
  default_glyph() call and unused Glyph import from main.rs
- Fix stale Behavior doc comment; update CLAUDE.md and ARCHITECTURE.md

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

kiln-egui/src/main.rs

@@ -10,7 +10,7 @@ mod render;
 
 use editor::{EditorState, EditorTab, show_editor_panel};
 use font::BitmapFont;
-use kiln_core::game::{FontSpec, GameState, Glyph, ObjectDef};
+use kiln_core::game::{FontSpec, GameState, ObjectDef};
 use kiln_core::map_file;
 use render::{
     DEFAULT_WINDOW_H, DEFAULT_WINDOW_W, MIN_WINDOW_H, MIN_WINDOW_W, board_origin, draw_board,
@@ -237,18 +237,7 @@ impl eframe::App for App {
                                     if self.editor.placing_object {
                                         // Placement mode: create a new object here if none exists.
                                         if board.object_index_at(cx, cy).is_none() {
-                                            board.objects.push(ObjectDef {
-                                                x: cx,
-                                                y: cy,
-                                                glyph: Glyph {
-                                                    tile: ObjectDef::default_glyph().tile,
-                                                    fg: ObjectDef::default_glyph().fg,
-                                                    bg: ObjectDef::default_glyph().bg,
-                                                },
-                                                passable: false,
-                                                opaque: true,
-                                                script_name: None,
-                                            });
+                                            board.objects.push(ObjectDef::new(cx, cy));
                                         }
                                         self.editor.placing_object = false;
                                     } else {