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/main.py

@@ -3071,7 +3071,7 @@ def _model_flow_nous(config, current_model="", args=None):
 
     # Verify credentials are still valid (catches expired sessions early)
     try:
-        creds = resolve_nous_runtime_credentials(min_key_ttl_seconds=5 * 60)
+        creds = resolve_nous_runtime_credentials()
     except Exception as exc:
         relogin = isinstance(exc, AuthError) and exc.relogin_required
         msg = format_auth_error(exc) if isinstance(exc, AuthError) else str(exc)
@@ -3105,7 +3105,6 @@ def _model_flow_nous(config, current_model="", args=None):
     if not free_tier:
         try:
             refreshed_creds = resolve_nous_runtime_credentials(
-                min_key_ttl_seconds=5 * 60,
                 force_refresh=True,
             )
             if refreshed_creds: