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>

web_interface/blueprints/api_v3.py

@@ -1,4 +1,4 @@
-from flask import Blueprint, request, jsonify, Response, send_from_directory
+from flask import Blueprint, request, jsonify, Response
 import json
 import os
 import re
@@ -17,10 +17,8 @@ logger = logging.getLogger(__name__)
 from src.web_interface.api_helpers import success_response, error_response, validate_request_json
 from src.web_interface.errors import ErrorCode
 from src.plugin_system.operation_types import OperationType
-from src.web_interface.logging_config import log_plugin_operation, log_config_change
 from src.web_interface.validators import (
-    validate_image_url, validate_file_upload, validate_mime_type,
-    validate_numeric_range, validate_string_length, sanitize_plugin_config
+    validate_file_upload
 )
 from src.error_aggregator import get_error_aggregator
 
@@ -4137,7 +4135,6 @@ def save_plugin_config():
                                             current_value = array_value  # Update for length check below
                                     except (ValueError, KeyError, TypeError) as e:
                                         logger.debug(f"Failed to convert {prop_key} to array: {e}")
-                                        pass
 
                                 # If it's an array, ensure correct types and check minItems
                                 if isinstance(current_value, list):