feat: v2.7.7 — File Explorer on workspaces and the user's home, clone with per-user git identity

- File Explorer (Files in the sidebar, /files; also from a workspace's Files
  tab, portalled so no panel clips it), laid out like GNOME Files: places
  (Home, workspaces, Trash), Back/Forward/Up, path bar, search, icon grid with
  image thumbnails or list, labelled New/Upload, selection action bar, hidden
  files behind Ctrl+H, right-click menus and the usual keys.
  Make, rename, move, copy (within a workspace, between workspaces, home ↔
  workspace), delete into a per-account trash restorable for 7 days, streamed
  upload of files and whole folders (≤ 500 MB a batch, Replace / Keep both /
  Skip on a taken name), download a file or a zip of anything.
  server/lib/file-explorer.js, /api/lanes/:id/fs/*, /api/homes/:who/fs/*.
- The user's home: every dot entry at its top stays hidden and refused
  (also via a symlink, download, zip or as a copy source); an admin may view
  other users' homes read-only, audited.
- write-as learns move/copy (re-run `sudo agenthub server install-system`).
- Hardening: a write to a workspace re-checks its owner by the live role;
  S3 keeps its server.conf if the file stops reading and a tmux call never
  falls back to the host's server; the AI Proxy gateway marks what it relays
  and the dashboard refuses it; a NUL in a pane's argv/env is refused.
- OpenAPI for the new routes (server/openapi-extra/files.js); docs (API,
  SERVER-MODE, CLAUDE.md) updated.

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

server/__tests__/server-s3-review5.test.js

@@ -572,6 +572,40 @@ describe("who a pane runs as", () => {
     }
   });
 
+  it("a demoted admin can still READ their host-folder workspace but no longer WRITE to it", async () => {
+    fs.mkdirSync(path.join(HOST, "w"), { recursive: true });
+    const lane = addLane(path.join(HOST, "w"), "boss");
+    auth.setRole("boss", "developer");
+    try {
+      assert.equal((await call("boss", "GET", `/api/lanes/${lane}`)).status, 200);
+      for (const [method, url, body] of [
+        ["POST", `/api/lanes/${lane}/up`, {}],
+        ["POST", `/api/lanes/${lane}/git/commit`, { message: "x" }],
+        ["PUT", `/api/lanes/${lane}/git/file`, { path: "a.txt", content: "x" }],
+        ["PATCH", `/api/workspaces/${lane}`, { title: "t" }],
+      ]) {
+        const r = await call("boss", method, url, body);
+        assert.equal(r.status, 409, `${method} ${url} ${JSON.stringify(r.body)}`);
+        assert.equal(r.body.error.code, "EOWNERFOLDER");
+      }
+    } finally {
+      auth.setRole("boss", "admin");
+    }
+    // Back to admin: the same write passes the guard again.
+    const ok = await call("boss", "PATCH", `/api/lanes/${lane}`, { title: "back" });
+    assert.equal(ok.status, 200, JSON.stringify(ok.body));
+  });
+
+  it("a member's own workspace writes are untouched by that check", async () => {
+    const r = await call("mia", "GET", "/api/lanes");
+    const mine = (r.body.lanes || []).find((l) =>
+      String(l.cwd).startsWith(path.join(USERS, "mia"))
+    );
+    if (!mine) return; // no member workspace in this fixture
+    const w = await call("mia", "PATCH", `/api/lanes/${mine.id}`, { title: "still mine" });
+    assert.notEqual(w.status, 409, JSON.stringify(w.body));
+  });
+
   it("a pane's cwd must be its workspace's account's (POST /api/run names the cwd)", async () => {
     const mine = addLane(path.join(MIA, "own"), "mia");
     assert.throws(