fix(node/nix): consolidate workspace lockfile + update all consumers

Consolidate per-package package-lock.json files into a single root-level
workspace lockfile.  Update all consumers:

- Nix: shared src/npmDeps/npmDepsHash in lib.nix; devshell hook stamps
  package.json paths then runs npm ci from root; individual .nix files
  use mkNpmPassthru attrs instead of per-package fetchNpmDeps.
- Python CLI: new _workspace_root() helper so _tui_need_npm_install,
  _make_tui_argv, _build_web_ui resolve lockfile/node_modules from the
  workspace root.
- Desktop: replace --force-build/mtime heuristic with content-hash build
  stamp (_compute_desktop_content_hash via pathspec).  Remove --force-build
  flag.
- Dockerfile: single root npm install; no per-directory lockfile copies.
- CI: nix-lockfile-fix and osv-scanner reference root package-lock.json;
  apps/dashboard → apps/desktop.
- Tests: new test_tui_npm_install.py; desktop stamp tests in
  test_gui_command.py; updated assertions in test_cmd_update.py,
  test_web_ui_build.py, test_dockerfile_pid1_reaping.py.
- Docs: remove --force-build from desktop flag table.

Deleted: apps/desktop/package-lock.json, ui-tui/package-lock.json,
ui-tui/packages/hermes-ink/package-lock.json, web/package-lock.json.

tests/hermes_cli/test_web_ui_build.py

@@ -69,7 +69,9 @@ class TestWebUIBuildNeeded:
     def test_returns_true_when_package_lock_newer_than_dist(self, tmp_path):
         web_dir, dist_dir = _make_web_dir(tmp_path)
         _touch(dist_dir / ".vite" / "manifest.json", offset=-10)
-        _touch(web_dir / "package-lock.json")
+        # With a single workspace root lockfile, the lockfile lives at the
+        # project root (tmp_path), not inside web_dir.
+        _touch(tmp_path / "package-lock.json")
         assert _web_ui_build_needed(web_dir) is True
 
     def test_returns_true_when_vite_config_newer_than_dist(self, tmp_path):