chore: remove unused imports and dead locals (ruff F401/F841 sweep)

Cleans F401 unused imports and F841 dead local assignments across
root *.py, agent/, hermes_cli/, tools/, gateway/, cron/, tui_gateway/
(tests/, plugins/, skills/ excluded).

Intentionally KEPT (false positives / test-patch surfaces):
- agent/transports/__init__.py package re-exports
- cli.py browser_connect re-exports (DEFAULT_BROWSER_CDP_URL area,
  used by tests/cli/test_cli_browser_connect.py)
- hermes_cli/main.py _prompt_auth_credentials_choice /
  _model_flow_bedrock_api_key (accessed via main_mod attr in tests)
- gateway/run.py aliased replay_cleanup + whatsapp_identity re-exports
  and _PORT_BINDING_PLATFORM_VALUES (test-referenced)
- hermes_cli/web_server.py get_running_pid (tests monkeypatch it) and
  _OAUTH_TOKEN_URL availability probe
- hermes_cli/config.py get_process_hermes_home re-export (noqa'd F811
  chain) and yaml availability-probe import
- hermes_cli/nous_subscription.py managed_nous_tools_enabled
  (tests patch hermes_cli.nous_subscription.managed_nous_tools_enabled)
- try/except ImportError availability probes (env_loader, tts_tool,
  mcp_tool, web_server anthropic OAuth block)
- tools/web_tools.py noqa F401 re-exports
- hermes_cli/setup_whatsapp_cloud.py:263 'proceed' skipped: possible
  missing-guard bug, flagged for separate review
- unused function parameters (signature changes out of scope)

Side-effect RHS calls preserved where only the binding was dead
(e.g. web_server proc = _spawn_hermes_action -> bare call).

hermes_cli/model_setup_flows.py

@@ -1981,7 +1981,6 @@ def _model_flow_kimi(config, current_model=""):
 
     provider_id = "kimi-coding"
     pconfig = PROVIDER_REGISTRY[provider_id]
-    key_env = pconfig.api_key_env_vars[0] if pconfig.api_key_env_vars else ""
     base_url_env = pconfig.base_url_env_var or ""
 
     # Step 1: Check / prompt for API key
@@ -2066,7 +2065,6 @@ def _model_flow_stepfun(config, current_model=""):
 
     provider_id = "stepfun"
     pconfig = PROVIDER_REGISTRY[provider_id]
-    key_env = pconfig.api_key_env_vars[0] if pconfig.api_key_env_vars else ""
     base_url_env = pconfig.base_url_env_var or ""
 
     existing_key, existing_source = _existing_api_key_for_model_flow(provider_id, pconfig)
@@ -2174,7 +2172,6 @@ def _model_flow_bedrock_api_key(config, region, current_model=""):
     from hermes_cli.config import (
         load_config,
         save_config,
-        get_env_value,
         save_env_value,
     )
     from hermes_cli.models import _PROVIDER_MODELS