refactor: Modularize Electron main process into single-responsibility components

Extract the monolithic main.ts (~1000 lines) into focused modules:

- electron/constants.ts - Window sizing, port defaults, filenames
- electron/state.ts - Shared state container
- electron/utils/ - Port availability and icon utilities
- electron/security/ - API key management
- electron/windows/ - Window bounds and main window creation
- electron/server/ - Backend and static server management
- electron/ipc/ - IPC handlers with shared channel constants

Benefits:
- Improved testability with isolated modules
- Better discoverability and maintainability
- Single source of truth for IPC channels (used by both main and preload)
- Clear separation of concerns

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/electron/ipc/shell-handlers.ts

@@ -0,0 +1,61 @@
+/**
+ * Shell IPC handlers
+ *
+ * Handles shell operations like opening external links and files.
+ */
+
+import { ipcMain, shell } from 'electron';
+import { IPC_CHANNELS } from './channels';
+
+/**
+ * Register shell IPC handlers
+ */
+export function registerShellHandlers(): void {
+  // Open external URL
+  ipcMain.handle(IPC_CHANNELS.SHELL.OPEN_EXTERNAL, async (_, url: string) => {
+    try {
+      await shell.openExternal(url);
+      return { success: true };
+    } catch (error) {
+      return { success: false, error: (error as Error).message };
+    }
+  });
+
+  // Open file path
+  ipcMain.handle(IPC_CHANNELS.SHELL.OPEN_PATH, async (_, filePath: string) => {
+    try {
+      await shell.openPath(filePath);
+      return { success: true };
+    } catch (error) {
+      return { success: false, error: (error as Error).message };
+    }
+  });
+
+  // Open file in editor (VS Code, etc.) with optional line/column
+  ipcMain.handle(
+    IPC_CHANNELS.SHELL.OPEN_IN_EDITOR,
+    async (_, filePath: string, line?: number, column?: number) => {
+      try {
+        // Build VS Code URL scheme: vscode://file/path:line:column
+        // This works on all platforms where VS Code is installed
+        // URL encode the path to handle special characters (spaces, brackets, etc.)
+        // Handle both Unix (/) and Windows (\) path separators
+        const normalizedPath = filePath.replace(/\\/g, '/');
+        const encodedPath = normalizedPath.startsWith('/')
+          ? '/' + normalizedPath.slice(1).split('/').map(encodeURIComponent).join('/')
+          : normalizedPath.split('/').map(encodeURIComponent).join('/');
+        let url = `vscode://file${encodedPath}`;
+        if (line !== undefined && line > 0) {
+          url += `:${line}`;
+          if (column !== undefined && column > 0) {
+            url += `:${column}`;
+          }
+        }
+        await shell.openExternal(url);
+        return { success: true };
+      } catch (error) {
+        return { success: false, error: (error as Error).message };
+      }
+    }
+  );
+}