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/hermes_cli/test_plugins_cmd.py

@@ -3,8 +3,6 @@
 from __future__ import annotations
 
 import logging
-import os
-import types
 from pathlib import Path
 from unittest.mock import MagicMock, patch
 
@@ -19,7 +17,6 @@ from hermes_cli.plugins_cmd import (
     _resolve_git_executable,
     _resolve_git_url,
     _sanitize_plugin_name,
-    plugins_command,
 )
 
 
@@ -259,7 +256,6 @@ class TestCmdInstall:
 
     def test_install_requires_identifier(self):
         from hermes_cli.plugins_cmd import cmd_install
-        import argparse
 
         with pytest.raises(SystemExit):
             cmd_install("")
@@ -544,7 +540,6 @@ class TestCopyExampleFiles:
     """Test example file copying."""
 
     def test_copies_example_files(self, tmp_path):
-        from hermes_cli.plugins_cmd import _copy_example_files
         from unittest.mock import MagicMock
 
         console = MagicMock()
@@ -560,7 +555,6 @@ class TestCopyExampleFiles:
         console.print.assert_called()
 
     def test_skips_existing_files(self, tmp_path):
-        from hermes_cli.plugins_cmd import _copy_example_files
         from unittest.mock import MagicMock
 
         console = MagicMock()
@@ -577,7 +571,6 @@ class TestCopyExampleFiles:
         assert real_file.read_text() == "existing: true"
 
     def test_handles_copy_error_gracefully(self, tmp_path):
-        from hermes_cli.plugins_cmd import _copy_example_files
         from unittest.mock import MagicMock, patch
 
         console = MagicMock()