fix: Resolve 21 ruff linting errors (SIM102, SIM117, B904, SIM113, B007)

Fixed all 21 linting errors identified in GitHub Actions:

SIM102 (7 errors - nested if statements):
- config_extractor.py:468 - Combined nested conditions
- config_validator.py (was B904, already fixed)
- pattern_recognizer.py:430,538,916 - Combined nested conditions
- test_example_extractor.py:365,412,460 - Combined nested conditions
- unified_skill_builder.py:1070 - Combined nested conditions

SIM117 (9 errors - multiple with statements):
- test_install_agent.py:418 - Combined with statements
- test_issue_219_e2e.py:278 - Combined with statements
- test_llms_txt_downloader.py:33,88 - Combined with statements
- test_skip_llms_txt.py:75,98,121,148,172,304 - Combined with statements

B904 (1 error - exception handling):
- config_validator.py:62 - Added 'from e' to exception chain

SIM113 (1 error - enumerate usage):
- doc_scraper.py:1068 - Removed unused 'completed' counter variable

B007 (1 error - unused loop variable):
- pdf_scraper.py:167 - Changed 'keywords' to '_' for unused variable

All changes improve code quality without altering functionality.
Tests: 1214 passed, 167 skipped (4 pre-existing failures unrelated)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/cli/config_extractor.py

@@ -466,24 +466,23 @@ class ConfigParser:
             tree = ast.parse(config_file.raw_content)
 
             for node in ast.walk(tree):
-                if isinstance(node, ast.Assign):
-                    # Get variable name and skip private variables
-                    if len(node.targets) == 1 and isinstance(node.targets[0], ast.Name) and not node.targets[0].id.startswith("_"):
-                        key = node.targets[0].id
+                # Get variable name and skip private variables
+                if isinstance(node, ast.Assign) and len(node.targets) == 1 and isinstance(node.targets[0], ast.Name) and not node.targets[0].id.startswith("_"):
+                    key = node.targets[0].id
 
-                        # Extract value
-                        try:
-                            value = ast.literal_eval(node.value)
-                            setting = ConfigSetting(
-                                key=key,
-                                value=value,
-                                value_type=self._infer_type(value),
-                                description=self._extract_python_docstring(node),
-                            )
-                            config_file.settings.append(setting)
-                        except (ValueError, TypeError):
-                            # Can't evaluate complex expressions
-                            pass
+                    # Extract value
+                    try:
+                        value = ast.literal_eval(node.value)
+                        setting = ConfigSetting(
+                            key=key,
+                            value=value,
+                            value_type=self._infer_type(value),
+                            description=self._extract_python_docstring(node),
+                        )
+                        config_file.settings.append(setting)
+                    except (ValueError, TypeError):
+                        # Can't evaluate complex expressions
+                        pass
 
         except SyntaxError as e:
             config_file.parse_errors.append(f"Python parse error: {str(e)}")