feat: convert file manager into a plugin

src/ui/tests/sidebar/rail-items.test.ts

@@ -48,6 +48,7 @@ describe("RAIL_ITEMS", () => {
     // Guards against a destination silently disappearing now that the rail,
     // the settings toggles, the sidebar titles and the mobile bar all read
     // from this one list.
+    // "sftp" moved to the file-manager plugin's own registerRailItem.
     expect(RAIL_ITEMS.map((item) => item.id)).toEqual([
       "hosts",
       "credentials",
@@ -58,7 +59,6 @@ describe("RAIL_ITEMS", () => {
       "quick-connect",
       "serial",
       "ssh-tools",
-      "sftp",
       "macros",
       "history",
       "session-logs",

src/ui/tests/sidebar/tree/HostItem/HostItem.test.tsx

@@ -219,16 +219,16 @@ describe("HostItem density parity", () => {
 
   it("learns repeated local actions and preloads the preferred host tool", () => {
     renderHostItem("comfortable");
-    const filesButton = screen.getByTitle("Files");
-    fireEvent.click(filesButton);
-    fireEvent.click(filesButton);
-    fireEvent.click(filesButton);
+    const tunnelButton = screen.getByTitle("Tunnel");
+    fireEvent.click(tunnelButton);
+    fireEvent.click(tunnelButton);
+    fireEvent.click(tunnelButton);
 
     const hostRow = screen.getByText("web-01").closest(".cursor-pointer");
     expect(hostRow).toBeTruthy();
     fireEvent.pointerEnter(hostRow!);
 
     expect(preloadTabSurfaceMock).toHaveBeenCalledWith("terminal");
-    expect(preloadTabSurfaceMock).toHaveBeenCalledWith("files");
+    expect(preloadTabSurfaceMock).toHaveBeenCalledWith("tunnel");
   });
 });