feat: convert file manager into a plugin

plugins/file-manager/tests/frontend/file-preview-preload.test.ts

@@ -0,0 +1,18 @@
+import { describe, expect, it } from "vitest";
+import { resolveFilePreviewKind } from "../../src/frontend/file-preview-preload";
+
+describe("resolveFilePreviewKind", () => {
+  it.each([
+    ["photo.webp", "image"],
+    ["movie.webm", "video"],
+    ["voice.m4a", "audio"],
+    ["README.md", "markdown"],
+    ["manual.pdf", "pdf"],
+    ["notes.txt", "text"],
+    ["app.tsx", "code"],
+    ["Dockerfile", "code"],
+    ["LICENSE", "unknown"],
+  ] as const)("classifies %s as %s", (filename, expected) => {
+    expect(resolveFilePreviewKind(filename)).toBe(expected);
+  });
+});