refactor: Modularize UI components and utilities

- Extract UI components into separate JS files
- Centralize configuration values in config.js
- Introduce a dedicated logger module
- Improve file tree drag-and-drop and undo functionality
- Refactor modal handling to a single manager
- Add URL routing support for SPA navigation
- Implement view mode for read-only access

static/js/event-bus.js

@@ -0,0 +1,126 @@
+/**
+ * Event Bus Module
+ * Provides a centralized event system for application-wide communication
+ * Allows components to communicate without tight coupling
+ */
+
+class EventBus {
+    constructor() {
+        /**
+         * Map of event names to arrays of listener functions
+         * @type {Object.<string, Function[]>}
+         */
+        this.listeners = {};
+    }
+
+    /**
+     * Register an event listener
+     * @param {string} event - The event name to listen for
+     * @param {Function} callback - The function to call when the event is dispatched
+     * @returns {Function} A function to unregister this listener
+     */
+    on(event, callback) {
+        if (!this.listeners[event]) {
+            this.listeners[event] = [];
+        }
+        this.listeners[event].push(callback);
+
+        // Return unsubscribe function
+        return () => this.off(event, callback);
+    }
+
+    /**
+     * Register a one-time event listener
+     * The listener will be automatically removed after being called once
+     * @param {string} event - The event name to listen for
+     * @param {Function} callback - The function to call when the event is dispatched
+     * @returns {Function} A function to unregister this listener
+     */
+    once(event, callback) {
+        const onceWrapper = (data) => {
+            callback(data);
+            this.off(event, onceWrapper);
+        };
+        return this.on(event, onceWrapper);
+    }
+
+    /**
+     * Unregister an event listener
+     * @param {string} event - The event name
+     * @param {Function} callback - The callback function to remove
+     */
+    off(event, callback) {
+        if (!this.listeners[event]) {
+            return;
+        }
+
+        this.listeners[event] = this.listeners[event].filter(
+            listener => listener !== callback
+        );
+
+        // Clean up empty listener arrays
+        if (this.listeners[event].length === 0) {
+            delete this.listeners[event];
+        }
+    }
+
+    /**
+     * Dispatch an event to all registered listeners
+     * @param {string} event - The event name to dispatch
+     * @param {any} data - The data to pass to the listeners
+     */
+    dispatch(event, data) {
+        if (!this.listeners[event]) {
+            return;
+        }
+
+        // Create a copy of the listeners array to avoid issues if listeners are added/removed during dispatch
+        const listeners = [...this.listeners[event]];
+        
+        listeners.forEach(callback => {
+            try {
+                callback(data);
+            } catch (error) {
+                Logger.error(`Error in event listener for "${event}":`, error);
+            }
+        });
+    }
+
+    /**
+     * Remove all listeners for a specific event
+     * If no event is specified, removes all listeners for all events
+     * @param {string} [event] - The event name (optional)
+     */
+    clear(event) {
+        if (event) {
+            delete this.listeners[event];
+        } else {
+            this.listeners = {};
+        }
+    }
+
+    /**
+     * Get the number of listeners for an event
+     * @param {string} event - The event name
+     * @returns {number} The number of listeners
+     */
+    listenerCount(event) {
+        return this.listeners[event] ? this.listeners[event].length : 0;
+    }
+
+    /**
+     * Get all event names that have listeners
+     * @returns {string[]} Array of event names
+     */
+    eventNames() {
+        return Object.keys(this.listeners);
+    }
+}
+
+// Create and export the global event bus instance
+const eventBus = new EventBus();
+
+// Make it globally available
+window.eventBus = eventBus;
+window.EventBus = EventBus;
+