fix: ruff lint errors (F541, F821, F401)

Author: ChidcGithub

backend/analyzers/security.py

@@ -3,6 +3,7 @@
 Detects SQL injection, unsafe deserialization, hardcoded secrets, etc.
 """
 import ast
+import os
 import re
 from typing import List, Dict, Optional
 from ..models.schemas import CodeIssue, SeverityLevel
@@ -376,7 +377,7 @@ def _check_command_injection(self, tree: ast.AST):
                         id=self._generate_issue_id("legacy_command"),
                         type="security",
                         severity=SeverityLevel.ERROR,
-                        message=f"Legacy module 'commands' is insecure and removed in Python 3",
+                        message="Legacy module 'commands' is insecure and removed in Python 3",
                         lineno=node.lineno,
                         suggestion="Use subprocess.run() with shell=False"
                     ))

backend/ast_parser/node_builder.py

@@ -5,7 +5,7 @@
 @link: github.com/chidcGithub
 """
 import ast
-from typing import Dict, List, Optional, Any, Set
+from typing import Dict, List, Optional, Any
 
 from ..models.schemas import ASTNode, NodeType
 from .node_styles import NODE_STYLES

backend/ast_parser/relationships.py

@@ -5,7 +5,7 @@
 @link: github.com/chidcGithub
 """
 import logging
-from typing import Dict, List, Optional, Set, Any
+from typing import Dict, List, Optional, Set
 
 from ..models.schemas import ASTNode, ASTEdge, NodeType, VariableInfo, CodeRelationship
 

backend/routers/analysis.py

@@ -6,13 +6,12 @@
 """
 import ast
 import logging
-from typing import Dict, List, Any
 
 from fastapi import APIRouter, HTTPException, status
 from pydantic import BaseModel
 
 from ..models.schemas import (
-    CodeInput, AnalysisResult, ComplexityMetrics, CodeIssue, SeverityLevel
+    CodeInput, AnalysisResult, ComplexityMetrics, SeverityLevel
 )
 from ..exceptions import CodeParsingError, CodeTooLargeError, AnalysisError
 from ..ast_parser import ASTParser, NodeMapper

backend/routers/ast_routes.py

@@ -4,7 +4,6 @@
 @author: Chidc
 @link: github.com/chidcGithub
 """
-import ast
 import logging
 from typing import Optional
 

backend/routers/learning.py

@@ -5,7 +5,7 @@
 @link: github.com/chidcGithub
 """
 import logging
-from typing import Dict, Any, List
+from typing import Dict, Any
 
 from fastapi import APIRouter