modernize re-added Vercel integrations: SDK 0.7.2, telemetry off, sibling-site wiring

- Bump vercel SDK pin 0.5.7 -> 0.7.2 (pyproject, lazy_deps) and regenerate uv.lock
- Disable the SDK's new default-on telemetry (VERCEL_TELEMETRY_DISABLED=1
  set before import, user-overridable) per the no-opt-out-telemetry policy
- Move _model_flow_ai_gateway into hermes_cli/model_setup_flows.py (god-file
  decomposition landed after the removal)
- Widen post-removal backend sets that vercel_sandbox missed: terminal_tool
  container_backend + _CONTAINER_BACKENDS, file_tools fallback set,
  env_probe._REMOTE_BACKENDS, approval._should_skip_container_guards,
  prompt_builder probe container_config
- Add terminal.vercel_runtime to config_defaults + TERMINAL_CONFIG_ENV_MAP
- Re-add vercel dependency group to nix #full variant (reverts #33773 workaround)
- Update restored tests to current contracts: upload-only credential sync-back
  (bcfc7458fa), registry-derived provider env list, parametrized backend fixture,
  drop tests superseded on main (slack wizard move #41112, nous status format)

tests/cli/test_cli_init.py

@@ -398,6 +398,9 @@ class TestRootLevelProviderOverride:
 
         assert cfg["model"]["provider"] == "opencode-go"
 
+    def test_root_base_url_used_as_fallback_when_model_base_url_missing(self, tmp_path, monkeypatch):
+        """Legacy root-level base_url still populates model.base_url in the CLI loader."""
+        import yaml
 
         hermes_home = tmp_path / ".hermes"
         hermes_home.mkdir()