Refactor main.rs into focused modules: render, editor, glyph_picker

Splits the flat 432-line main.rs into four modules so each file has one
clear job: render.rs owns layout constants and drawing primitives,
editor.rs owns EditorTab/EditorState and the side panel, glyph_picker.rs
owns the floating picker dialog with a decoupled (open, glyph) interface,
and main.rs is reduced to AppMode, App, and the frame loop (~150 lines).

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

src/editor.rs

@@ -0,0 +1,117 @@
+use eframe::egui;
+use egui::{Align2, FontId, Sense, vec2};
+
+use crate::game::{Archetype, Board, Glyph, ALL_ARCHETYPES};
+use crate::render::{CELL_H, CELL_W, PALETTE_PANEL_W};
+
+/// Which tab is active in the editor side panel.
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub(crate) enum EditorTab {
+    /// Archetype + glyph palette for painting cells.
+    Palette,
+    /// Board-level properties (placeholder).
+    Board,
+    /// World-level properties (placeholder).
+    World,
+}
+
+/// Transient editor state. Only meaningful when the app is in Edit mode.
+pub(crate) struct EditorState {
+    /// The archetype that will be stamped when the user clicks a cell.
+    pub(crate) selected: Archetype,
+    /// The glyph (character + colors) to stamp. Independent of the archetype's default.
+    pub(crate) glyph: Glyph,
+    /// Whether the glyph picker dialog is currently open.
+    pub(crate) glyph_picker_open: bool,
+    /// Which side-panel tab is currently shown.
+    pub(crate) tab: EditorTab,
+}
+
+impl EditorState {
+    /// Creates editor state with `Wall` selected and the picker closed.
+    pub(crate) fn new() -> Self {
+        Self {
+            selected: Archetype::Wall,
+            glyph: Archetype::Wall.default_glyph(),
+            glyph_picker_open: false,
+            tab: EditorTab::Palette,
+        }
+    }
+}
+
+/// Renders the editor side panel (must be called before `CentralPanel`).
+///
+/// Shows tab bar (Palette / Board / World) and, on the Palette tab, the
+/// scrollable archetype list and current-glyph preview button.
+pub(crate) fn show_editor_panel(ctx: &egui::Context, editor: &mut EditorState, _board: &Board) {
+    egui::SidePanel::right("palette_panel")
+        .resizable(true)
+        .default_width(PALETTE_PANEL_W)
+        .show(ctx, |ui| {
+            // Tab bar
+            ui.horizontal(|ui| {
+                ui.selectable_value(&mut editor.tab, EditorTab::Palette, "Palette");
+                ui.selectable_value(&mut editor.tab, EditorTab::Board,   "Board");
+                ui.selectable_value(&mut editor.tab, EditorTab::World,   "World");
+            });
+            ui.separator();
+
+            match editor.tab {
+                EditorTab::Palette => {
+                    ui.label("Element");
+
+                    // Scrollable archetype list; shows at most 5 rows before scrolling.
+                    let row_h = CELL_H + ui.spacing().item_spacing.y;
+                    egui::ScrollArea::vertical()
+                        .max_height(row_h * 5.0)
+                        .id_salt("arch_list")
+                        .show(ui, |ui| {
+                            for &archetype in ALL_ARCHETYPES {
+                                let is_selected = editor.selected == archetype;
+                                let glyph = archetype.default_glyph();
+                                ui.horizontal(|ui| {
+                                    let (r, cell_resp) = ui.allocate_exact_size(
+                                        vec2(CELL_W, CELL_H), Sense::click());
+                                    {
+                                        let p = ui.painter();
+                                        p.rect_filled(r, 0.0, glyph.bg);
+                                        p.text(r.center(), Align2::CENTER_CENTER,
+                                            glyph.ch, FontId::monospace(CELL_H), glyph.fg);
+                                    }
+                                    let label_resp =
+                                        ui.selectable_label(is_selected, archetype.name());
+                                    if cell_resp.clicked() || label_resp.clicked() {
+                                        editor.selected = archetype;
+                                        editor.glyph    = archetype.default_glyph();
+                                    }
+                                });
+                            }
+                        });
+
+                    ui.separator();
+
+                    ui.label("Glyph");
+                    // Paint a preview cell showing the current glyph, sized like a board cell.
+                    let (cell_rect, glyph_btn) =
+                        ui.allocate_exact_size(vec2(CELL_W, CELL_H), Sense::click());
+                    {
+                        let p = ui.painter();
+                        p.rect_filled(cell_rect, 0.0, editor.glyph.bg);
+                        p.text(
+                            cell_rect.center(),
+                            Align2::CENTER_CENTER,
+                            editor.glyph.ch,
+                            FontId::monospace(CELL_H),
+                            editor.glyph.fg,
+                        );
+                    }
+                    if glyph_btn.clicked() {
+                        editor.glyph_picker_open = true;
+                    }
+                }
+                EditorTab::Board => {}
+                EditorTab::World => {}
+            }
+        });
+}
+