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/web_server.py

@@ -2065,7 +2065,6 @@ async def _start_device_code_flow(provider_id: str) -> Dict[str, Any]:
 def _nous_poller(session_id: str) -> None:
     """Background poller that drives a Nous device-code flow to completion."""
     from hermes_cli.auth import (
-        NOUS_INFERENCE_AUTH_MODE_FRESH,
         _poll_for_token,
         refresh_nous_oauth_from_state,
     )
@@ -2111,10 +2110,8 @@ def _nous_poller(session_id: str) -> None:
         }
         full_state = refresh_nous_oauth_from_state(
             auth_state,
-            min_key_ttl_seconds=300,
             timeout_seconds=15.0,
             force_refresh=False,
-            inference_auth_mode=NOUS_INFERENCE_AUTH_MODE_FRESH,
         )
         from hermes_cli.auth import persist_nous_credentials
         persist_nous_credentials(full_state)