feat(gui): egui skeleton with dark theme

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

crates/gui/src/app.rs

@@ -0,0 +1,43 @@
+pub struct LogViewerApp;
+
+impl Default for LogViewerApp {
+    fn default() -> Self {
+        Self
+    }
+}
+
+impl eframe::App for LogViewerApp {
+    fn ui(&mut self, ui: &mut egui::Ui, _frame: &mut eframe::Frame) {
+        egui::Panel::top("menu_bar").show_inside(ui, |ui| {
+            egui::MenuBar::new().ui(ui, |ui| {
+                ui.menu_button("File", |ui| {
+                    if ui.button("Open").clicked() {
+                        // TODO: file open dialog
+                    }
+                    if ui.button("Quit").clicked() {
+                        // TODO: quit
+                    }
+                });
+                ui.menu_button("Edit", |ui| {
+                    if ui.button("Find (Ctrl+F)").clicked() {
+                        // TODO: find
+                    }
+                });
+            });
+        });
+
+        egui::Panel::bottom("status_bar").show_inside(ui, |ui| {
+            ui.horizontal(|ui| {
+                ui.label("Ready");
+            });
+        });
+
+        egui::CentralPanel::default().show_inside(ui, |ui| {
+            ui.vertical_centered(|ui| {
+                ui.add_space(100.0);
+                ui.heading("Log Viewer");
+                ui.label("Open a file to get started (File → Open)");
+            });
+        });
+    }
+}

crates/gui/src/main.rs

@@ -1 +1,21 @@
-fn main() {}
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+mod app;
+
+fn main() -> eframe::Result {
+    let options = eframe::NativeOptions {
+        viewport: egui::ViewportBuilder::default()
+            .with_inner_size([1200.0, 800.0])
+            .with_min_inner_size([600.0, 400.0]),
+        ..Default::default()
+    };
+
+    eframe::run_native(
+        "Log Viewer",
+        options,
+        Box::new(|cc| {
+            cc.egui_ctx.set_visuals(egui::Visuals::dark());
+            Ok(Box::new(app::LogViewerApp))
+        }),
+    )
+}