feat: add file explorer with tree view and IDE layout

Backend: editor service for directory tree reading and file CRUD,
editor routes at /api/editor with path traversal protection.

Frontend: FileExplorer tree component with expand/collapse directories,
IDELayout with sidebar + header + outlet, wired into App routing.
Editor now receives state as props from App for cross-component file loading.

packages/frontend/src/pages/Editor.tsx

@@ -1,9 +1,18 @@
 import { useCallback, useMemo } from "react";
 import { MonacoEditor } from "../components/editor/MonacoEditor";
 import { EditorTabs } from "../components/editor/EditorTabs";
-import { useEditorState } from "../hooks/useEditorState";
 
-export function Editor() {
+interface EditorProps {
+  editorState: ReturnType<typeof import("../hooks/useEditorState").useEditorState>;
+}
+
+function displayName(tabKey: string): string {
+  const parts = tabKey.split(":");
+  const filePath = parts.length > 1 ? parts.slice(1).join(":") : tabKey;
+  return filePath.split("/").pop() ?? filePath;
+}
+
+export function Editor({ editorState }: EditorProps) {
   const {
     openTabs,
     activeTab,
@@ -12,7 +21,7 @@ export function Editor() {
     closeFile,
     updateContent,
     getContent,
-  } = useEditorState();
+  } = editorState;
 
   const tabs = useMemo(
     () =>
@@ -24,6 +33,11 @@ export function Editor() {
   );
 
   const activeContent = activeTab ? (getContent(activeTab) ?? "") : "";
+  const activeFilePath = activeTab
+    ? activeTab.includes(":")
+      ? activeTab.split(":").slice(1).join(":")
+      : activeTab
+    : "";
 
   const handleChange = useCallback(
     (value: string) => {
@@ -35,7 +49,7 @@ export function Editor() {
   );
 
   return (
-    <div className="flex h-screen flex-col" style={{ backgroundColor: "var(--forge-bg)" }}>
+    <div className="flex h-full flex-col" style={{ backgroundColor: "var(--forge-bg)" }}>
       <EditorTabs
         tabs={tabs}
         activeTab={activeTab}
@@ -46,7 +60,7 @@ export function Editor() {
         {activeTab ? (
           <MonacoEditor
             key={activeTab}
-            filePath={activeTab}
+            filePath={activeFilePath}
             content={activeContent}
             onChange={handleChange}
           />