chore: prune unused imports and duplicate import redefinitions

Remove unused imports (F401) and duplicate/shadowed import
redefinitions (F811) across the codebase using ruff's safe
autofixes. No behavioral changes -- imports only.

- ~1400 safe autofixes applied across 644 files (net -1072 lines)
- __init__.py re-exports preserved (excluded from F401 removal so
  public re-export surfaces stay intact)
- Re-exports that are imported or monkeypatched by tests but look
  unused in their defining module are kept with explicit # noqa:
  F401 (gateway/run.py load_dotenv; run_agent re-exports from
  agent.message_sanitization, agent.context_compressor,
  agent.retry_utils, agent.prompt_builder, agent.process_bootstrap,
  agent.codex_responses_adapter)
- Unsafe F841 (unused-variable) fixes deliberately skipped -- those
  can change behavior when the RHS has side effects
- ruff lints remain disabled in pyproject.toml (only PLW1514 is
  selected); this is a one-time cleanup, not a config change

Verification:
- python -m compileall: clean
- pytest --collect-only: all 27161 tests collect (zero import errors)
- core entry points import clean (run_agent, model_tools, cli,
  toolsets, hermes_state, batch_runner, gateway)
- static scan: every name any test imports directly from an edited
  module still resolves

tests/agent/test_auxiliary_client.py

@@ -2,9 +2,7 @@
 
 import json
 import logging
-import os
 import time
-from pathlib import Path
 from types import SimpleNamespace
 from unittest.mock import patch, MagicMock, AsyncMock
 
@@ -609,7 +607,7 @@ class TestExpiredCodexFallback:
         monkeypatch.setenv("ANTHROPIC_TOKEN", "sk-ant-oat01-test-fallback")
         with patch("agent.anthropic_adapter.build_anthropic_client") as mock_build:
             mock_build.return_value = MagicMock()
-            from agent.auxiliary_client import _resolve_auto, AnthropicAuxiliaryClient
+            from agent.auxiliary_client import _resolve_auto
             client, model = _resolve_auto()
             # Should NOT be Codex, should be Anthropic (or another available provider)
             assert not isinstance(client, type(None)), "Should find a provider after expired Codex"
@@ -696,7 +694,7 @@ class TestExpiredCodexFallback:
              patch("agent.anthropic_adapter.build_anthropic_client") as mock_build, \
              patch("agent.auxiliary_client._select_pool_entry", return_value=(False, None)):
             mock_build.return_value = MagicMock()
-            from agent.auxiliary_client import _try_anthropic, AnthropicAuxiliaryClient
+            from agent.auxiliary_client import _try_anthropic
             client, model = _try_anthropic()
             assert client is not None, "Should resolve token"
             adapter = client.chat.completions
@@ -751,7 +749,7 @@ class TestExpiredCodexFallback:
         monkeypatch.delenv("ANTHROPIC_TOKEN", raising=False)
         with patch("agent.anthropic_adapter.build_anthropic_client") as mock_build:
             mock_build.return_value = MagicMock()
-            from agent.auxiliary_client import _try_anthropic, AnthropicAuxiliaryClient
+            from agent.auxiliary_client import _try_anthropic
             client, model = _try_anthropic()
             assert client is not None
             adapter = client.chat.completions