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.

agent/credential_pool.py

@@ -22,7 +22,6 @@ from agent.credential_persistence import (
 import hermes_cli.auth as auth_mod
 from hermes_cli.auth import (
     CODEX_ACCESS_TOKEN_REFRESH_SKEW_SECONDS,
-    DEFAULT_AGENT_KEY_MIN_TTL_SECONDS,
     PROVIDER_REGISTRY,
     _auth_store_lock,
     _codex_access_token_is_expiring,
@@ -932,8 +931,6 @@ class CredentialPool:
                 if synced is not entry:
                     entry = synced
                 auth_mod.resolve_nous_runtime_credentials(
-                    min_key_ttl_seconds=DEFAULT_AGENT_KEY_MIN_TTL_SECONDS,
-                    inference_auth_mode=auth_mod.NOUS_INFERENCE_AUTH_MODE_AUTO,
                     force_refresh=force,
                 )
                 updated = self._sync_nous_entry_from_auth_store(entry)