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_session_browse.py

@@ -6,11 +6,9 @@ Covers:
 - Argument parser registration
 """
 
-import os
 import time
-from unittest.mock import MagicMock, patch, call
+from unittest.mock import MagicMock, patch
 
-import pytest
 
 from hermes_cli.main import _session_browse_picker
 
@@ -249,7 +247,6 @@ class TestCursesBrowse:
 
     def _run_with_keys(self, sessions, key_sequence):
         """Simulate running the curses picker with a given key sequence."""
-        import curses
 
         # Build a mock stdscr that returns keys from the sequence
         mock_stdscr = MagicMock()
@@ -305,7 +302,6 @@ class TestCursesBrowse:
 
     def test_type_to_filter_then_enter(self):
         """Typing characters filters the list, Enter selects from filtered."""
-        import curses
         sessions = [
             {"id": "s1", "source": "cli", "title": "Alpha project", "preview": "", "last_active": time.time()},
             {"id": "s2", "source": "cli", "title": "Beta project", "preview": "", "last_active": time.time()},
@@ -325,7 +321,6 @@ class TestCursesBrowse:
 
     def test_backspace_removes_filter_char(self):
         """Backspace removes the last character from the filter."""
-        import curses
         sessions = [
             {"id": "s1", "source": "cli", "title": "Alpha", "preview": "", "last_active": time.time()},
             {"id": "s2", "source": "cli", "title": "Beta", "preview": "", "last_active": time.time()},
@@ -337,7 +332,6 @@ class TestCursesBrowse:
 
     def test_escape_clears_filter_first(self):
         """First Esc clears the search text, second Esc exits."""
-        import curses
         sessions = _make_sessions(3)
         # Type "ab" then Esc (clears filter) then Enter (selects first)
         keys = [ord('a'), ord('b'), 27, 10]
@@ -391,11 +385,9 @@ class TestSessionBrowseArgparse:
 
     def test_browse_subcommand_exists(self):
         """hermes sessions browse should be parseable."""
-        from hermes_cli.main import main as _main_entry
 
         # We can't run main(), but we can import and test the parser setup
         # by checking that argparse doesn't error on "sessions browse"
-        import argparse
         # Re-create the parser portion
         # Instead, let's just verify the import works and the function exists
         from hermes_cli.main import _session_browse_picker