feat(server-mode): native-like folder browser, a developer kept to their own folder, no password minimum

- Folder browser (the Browse fallback for a remote browser): back/forward/up,
  a clickable breadcrumb that becomes a path field (Ctrl+L), Places (Home,
  the user's workspaces, recent picks), a filter, Name/Modified columns,
  Show hidden and New folder. A click selects; a double-click or Enter
  opens a folder or picks a file; Backspace goes up; typing jumps to a name.
- GET /api/lanes/browse: `hidden=1` (never the dot entries at the top of a
  non-admin's own folder), each entry's `mtime`, the answer's `home`.
- POST /api/lanes/browse/mkdir: one plain folder name inside an existing
  folder; a non-admin only in their own folder, none in server mode without
  one; under S3 a member's folder is made as the member.
- scope.ownFolder falls back to server.conf's USERS_ROOT under S3, so a
  settings file without AGENTHUB_USERS_ROOT no longer opens the host's home
  to every developer.
- Passwords: any non-empty password is accepted (no 8-character minimum).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/__tests__/server-mode-user-admin.test.js

@@ -94,12 +94,18 @@ describe("managing accounts from the dashboard", () => {
     });
     assert.equal(dup.status, 409);
     assert.equal(dup.body.error.code, "EEXISTS");
+    // No minimum length — only an empty password is refused.
+    const empty = await call("POST", "/api/users", {
+      cookie: boss,
+      body: { username: "zed", password: "", currentPassword: BOSS_PASS },
+    });
+    assert.equal(empty.status, 400);
+    assert.equal(empty.body.error.code, "EBADPASSWORD");
     const short = await call("POST", "/api/users", {
       cookie: boss,
-      body: { username: "zed", password: "short", currentPassword: BOSS_PASS },
+      body: { username: "zed", password: "1", currentPassword: BOSS_PASS },
     });
-    assert.equal(short.status, 400);
-    assert.equal(short.body.error.code, "EBADPASSWORD");
+    assert.equal(short.status, 201);
   });
 
   it("refuses without the admin's password, or with a wrong one", async () => {