refactor(auth): remove vestigial Nous min_key_ttl/inference_auth_mode params

After the legacy session-key path was removed, two parameters became dead
surface on the Nous runtime-resolution chain:

- min_key_ttl_seconds: del'd inside refresh_nous_oauth_pure and pass-through /
  telemetry-only in refresh_nous_oauth_from_state, _try_import_shared_nous_state,
  _nous_device_code_login, and resolve_nous_runtime_credentials. It controlled the
  now-deleted agent-key mint TTL and drives no behavior.
- inference_auth_mode: with the legacy mode gone, AUTO and FRESH are behaviorally
  identical; the value only fed _normalize_nous_inference_auth_mode validation and
  oauth trace output, never a branch.

Removing inference_auth_mode orphaned its whole supporting cluster
(NOUS_INFERENCE_AUTH_MODE_AUTO/FRESH, NOUS_INFERENCE_AUTH_MODES,
_normalize_nous_inference_auth_mode), and dropping min_key_ttl_seconds orphaned
DEFAULT_AGENT_KEY_MIN_TTL_SECONDS — all deleted here.

Updated every caller (run_agent, auxiliary_client, credential_pool, proxy adapter,
runtime_provider, web_server, main, auth_commands, setup) and pruned the matching
test kwargs. Deleted two tests that exercised the removed surface
(test_legacy_auth_mode_is_rejected, test_try_refresh_..._accepts_explicit_auth_mode).

No behavior change: net -134 LOC of dead code.

hermes_cli/auth_commands.py

@@ -272,9 +272,6 @@ def auth_add_command(args) -> None:
                 print("Rehydrating Nous session from shared credentials...")
                 rehydrated = auth_mod._try_import_shared_nous_state(
                     timeout_seconds=getattr(args, "timeout", None) or 15.0,
-                    min_key_ttl_seconds=max(
-                        60, int(getattr(args, "min_key_ttl_seconds", 5 * 60))
-                    ),
                 )
                 if rehydrated is not None:
                     custom_label = (getattr(args, "label", None) or "").strip() or None
@@ -297,7 +294,6 @@ def auth_add_command(args) -> None:
             timeout_seconds=getattr(args, "timeout", None) or 15.0,
             insecure=bool(getattr(args, "insecure", False)),
             ca_bundle=getattr(args, "ca_bundle", None),
-            min_key_ttl_seconds=max(60, int(getattr(args, "min_key_ttl_seconds", 5 * 60))),
         )
         # Honor `--label <name>` so nous matches other providers' UX.  The
         # helper embeds this into providers.nous so that label_from_token