fix: remove unused imports and bare exception aliases (pyflakes F401/F841)

Remove unused imports across 86 files in src/, web_interface/, test/,
and scripts/ using autoflake. No logic changes — only dead import
statements and unused names in from-imports are removed.

Also remove bare exception aliases where the variable is never
referenced in the handler body:
- src/cache/disk_cache.py: except (IOError, OSError, PermissionError) as e
- src/cache_manager.py: except (OSError, IOError, PermissionError) as perm_error
- src/plugin_system/resource_monitor.py: except Exception as e
- web_interface/app.py: except Exception as read_err

86 files changed, 205 lines removed, 18 pre-existing test failures unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/test_error_aggregator.py

@@ -9,11 +9,8 @@ Tests:
 - Thread safety
 """
 
-import pytest
-import time
 from datetime import datetime, timedelta
 from pathlib import Path
-from unittest.mock import Mock, patch
 import threading
 import sys
 
@@ -29,7 +26,7 @@ from src.error_aggregator import (
     get_error_aggregator,
     record_error
 )
-from src.exceptions import PluginError, ConfigError
+from src.exceptions import PluginError
 
 
 class TestErrorRecording: