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.

.github/workflows/osv-scanner.yml

@@ -28,7 +28,6 @@ on:
       - 'package.json'
       - 'package-lock.json'
       - 'ui-tui/package.json'
-      - 'ui-tui/package-lock.json'
       - 'website/package.json'
       - 'website/package-lock.json'
       - '.github/workflows/osv-scanner.yml'
@@ -39,7 +38,6 @@ on:
       - 'pyproject.toml'
       - 'package.json'
       - 'package-lock.json'
-      - 'ui-tui/package-lock.json'
       - 'website/package-lock.json'
   schedule:
     # Weekly scan against main — catches CVEs published after merge for
@@ -62,6 +60,6 @@ jobs:
       # the three sources of truth and skip vendored / test / worktree dirs.
       scan-args: |-
         --lockfile=uv.lock
-        --lockfile=ui-tui/package-lock.json
+        --lockfile=package-lock.json
         --lockfile=website/package-lock.json
       fail-on-vuln: false