fix: Remove duplicate import os statements causing UnboundLocalError

## Critical Bugs Fixed

### 1. UnboundLocalError in AI Enhancement Modules (BLOCKING)
**Issue**: Duplicate `import os` statements inside conditional blocks caused
UnboundLocalError when accessing os.environ before the import was reached.

**Files Fixed**:
- src/skill_seekers/cli/guide_enhancer.py (lines 92, 112)
- src/skill_seekers/cli/ai_enhancer.py (line 77)
- src/skill_seekers/cli/config_enhancer.py (line 82)

**Root Cause**: `os` was already imported at file top, but re-imported inside
conditional blocks, creating a local variable scope issue.

**Solution**: Removed duplicate import statements - os is already available
from the top-level import.

**Impact**: Fixed 30 failing guide_enhancer tests

### 2. PDF Scraper Test Expectations (BREAKING CHANGE)
**Issue**: Tests expected old keyword-based categorization behavior, but PR
introduced new single-file strategy for single PDF sources.

**Files Fixed**:
- tests/test_pdf_scraper.py (5 tests updated)

**Tests Updated**:
1. test_categorize_by_keywords
2. test_build_skill_creates_reference_files
3. test_code_blocks_included_in_references
4. test_high_quality_code_preferred
5. test_image_references_in_markdown

**Solution**: Updated test expectations to match new single-file strategy
behavior (single PDF → single category named after PDF basename).

**Impact**: Fixed 5 failing PDF scraper tests

## Test Results

**Before Fixes**: 35 tests failing
**After Fixes**: 130 tests passing, 5 skipped ✅

### Tested Modules:
- ✅ PDF scraper (18 tests)
- ✅ Guide enhancer (30 tests)
- ✅ All adaptors (82 tests)

## Verification

```bash
pytest tests/test_pdf_scraper.py tests/test_guide_enhancer.py tests/test_adaptors/ -v
# Result: 130 passed, 5 skipped in 1.11s
```

## Notes

The original PR features (GLM-4.7 support + PDF scraper improvements) are
excellent and working correctly. These fixes only address the import scoping
bug introduced during implementation and update tests for the new behavior.

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

tests/test_pdf_scraper.py

@@ -114,9 +114,11 @@ class TestCategorization(unittest.TestCase):
 
         categories = converter.categorize_content()
 
-        # Should have both categories
-        self.assertIn("getting_started", categories)
-        self.assertIn("api", categories)
+        # With single PDF source, should use single-file strategy
+        # Category named after PDF basename (test.pdf -> test)
+        self.assertIn("test", categories)
+        self.assertEqual(len(categories), 1)
+        self.assertEqual(len(categories["test"]["pages"]), 2)
 
     def test_categorize_by_chapters(self):
         """Test categorization using chapter information"""
@@ -234,17 +236,12 @@ class TestSkillBuilding(unittest.TestCase):
             "total_pages": 2,
         }
 
-        converter.categories = {
-            "getting_started": [converter.extracted_data["pages"][0]],
-            "api": [converter.extracted_data["pages"][1]],
-        }
-
         converter.build_skill()
 
         # Check reference files exist
+        # With single PDF source, uses single-file strategy (named after PDF basename)
         refs_dir = Path(self.temp_dir) / "test_skill" / "references"
-        self.assertTrue((refs_dir / "getting_started.md").exists())
-        self.assertTrue((refs_dir / "api.md").exists())
+        self.assertTrue((refs_dir / "test.md").exists())
         self.assertTrue((refs_dir / "index.md").exists())
 
 
@@ -289,12 +286,11 @@ class TestCodeBlockHandling(unittest.TestCase):
             "total_pages": 1,
         }
 
-        converter.categories = {"examples": [converter.extracted_data["pages"][0]]}
-
         converter.build_skill()
 
         # Check code block in reference file
-        ref_file = Path(self.temp_dir) / "test_skill" / "references" / "examples.md"
+        # With single PDF source, uses single-file strategy (named after PDF basename)
+        ref_file = Path(self.temp_dir) / "test_skill" / "references" / "test.md"
         content = ref_file.read_text()
 
         self.assertIn("```python", content)
@@ -329,10 +325,10 @@ class TestCodeBlockHandling(unittest.TestCase):
             "total_pages": 1,
         }
 
-        converter.categories = {"examples": [converter.extracted_data["pages"][0]]}
         converter.build_skill()
 
-        ref_file = Path(self.temp_dir) / "test_skill" / "references" / "examples.md"
+        # With single PDF source, uses single-file strategy (named after PDF basename)
+        ref_file = Path(self.temp_dir) / "test_skill" / "references" / "test.md"
         content = ref_file.read_text()
 
         # High quality code should be included
@@ -422,11 +418,11 @@ class TestImageHandling(unittest.TestCase):
             "total_pages": 1,
         }
 
-        converter.categories = {"architecture": [converter.extracted_data["pages"][0]]}
         converter.build_skill()
 
         # Check markdown has image reference
-        ref_file = Path(self.temp_dir) / "test_skill" / "references" / "architecture.md"
+        # With single PDF source, uses single-file strategy (named after PDF basename)
+        ref_file = Path(self.temp_dir) / "test_skill" / "references" / "test.md"
         content = ref_file.read_text()
 
         self.assertIn("![", content)  # Markdown image syntax