fix(packaging): ship locales/ i18n catalogs in wheel, sdist, and Nix (#38383)

* fix(packaging): ship locales/ i18n catalogs in wheel, sdist, and Nix

locales/ is a bare data dir (no __init__.py), invisible to packages.find
and package-data. Sealed installs (pip wheel, Nix store venv) dropped it,
so gateway/CLI commands rendered raw i18n keys like
gateway.reset.header_default.

- pyproject: [tool.setuptools.data-files] locales = ["locales/*.yaml"] (wheel)
- MANIFEST.in: graft locales (sdist)
- agent/i18n._locales_dir: env override -> source -> sysconfig data scheme
- nix/hermes-agent.nix: copy locales into the store + set HERMES_BUNDLED_LOCALES
  as defense-in-depth. The wheel's data-files already materialize into the
  uv2nix venv, so resolution works with no env var; the override pins the
  store path against a future uv2nix change that could drop data-files.
- tests: metadata regression, wheel + sdist build-install smoke tests, and a
  bundled-locales flake check that verifies BOTH the wrapper override and the
  env-var-less data-files path. Smoke test wired into CI.

Closes #23943, #27632, #35374.
Supersedes #23966, #27716, #30261, #33841, #35429, #35494, #35735, #36697.

* test: cap locale e2e timeout, tighten catalog count guard

The two wheel/sdist e2e tests inherit the global --timeout=30 from
addopts; a cold-CI run (isolated build env + venv create + network pip
install) can plausibly exceed it. Add @pytest.mark.timeout(300) so they
don't ride the unit-test budget and flake intermittently.

Also assert the shipped catalog count equals len(SUPPORTED_LANGUAGES)
instead of a hardcoded >=16 floor, so the guard self-updates and trips
on a single dropped catalog (not just a fully-empty graft).

.github/workflows/tests.yml

@@ -171,6 +171,11 @@ jobs:
           source .venv/bin/activate
           uv pip install -e ".[all,dev]"
 
+      - name: Packaged-wheel i18n smoke test
+        run: |
+          source .venv/bin/activate
+          python -m pytest -m integration tests/test_wheel_locales_e2e.py -v
+
       - name: Run e2e tests
         run: |
           source .venv/bin/activate