feat: convert file manager into a plugin

plugins/file-manager/tests/frontend/hooks/usePaneWidth.test.ts

@@ -0,0 +1,50 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { act, renderHook } from "@testing-library/react";
+import { usePaneWidth } from "../../../src/frontend/hooks/usePaneWidth";
+
+const KEY = "test:pane-width";
+
+function mouse(type: string, clientX: number) {
+  document.dispatchEvent(new MouseEvent(type, { clientX, bubbles: true }));
+}
+
+const opts = { storageKey: KEY, defaultWidth: 224, minWidth: 160 };
+
+describe("usePaneWidth", () => {
+  beforeEach(() => localStorage.clear());
+
+  it("starts at the default and restores a stored width", () => {
+    expect(renderHook(() => usePaneWidth(opts)).result.current.width).toBe(224);
+    localStorage.setItem(KEY, "300");
+    expect(renderHook(() => usePaneWidth(opts)).result.current.width).toBe(300);
+    localStorage.setItem(KEY, "10"); // below min → ignored
+    expect(renderHook(() => usePaneWidth(opts)).result.current.width).toBe(224);
+  });
+
+  it("follows the drag, clamps to the minimum, and persists on release", () => {
+    const { result } = renderHook(() => usePaneWidth(opts));
+    act(() => {
+      result.current.startResize({
+        clientX: 400,
+        preventDefault() {},
+        stopPropagation() {},
+      } as unknown as React.MouseEvent);
+    });
+    expect(result.current.isResizing).toBe(true);
+    act(() => mouse("mousemove", 460));
+    expect(result.current.width).toBe(284);
+    act(() => mouse("mousemove", 100));
+    expect(result.current.width).toBe(160);
+    act(() => mouse("mouseup", 100));
+    expect(result.current.isResizing).toBe(false);
+    expect(localStorage.getItem(KEY)).toBe("160");
+  });
+
+  it("resets to the default", () => {
+    localStorage.setItem(KEY, "300");
+    const { result } = renderHook(() => usePaneWidth(opts));
+    act(() => result.current.resetWidth());
+    expect(result.current.width).toBe(224);
+    expect(localStorage.getItem(KEY)).toBe("224");
+  });
+});