fix: Add package installation check and fix test imports (Task 2.1)

Fixes test import errors in 7 test files that failed without package installed.

**Changes:**

1. **tests/conftest.py** - Added pytest_configure() hook
   - Checks if skill_seekers package is installed before running tests
   - Shows helpful error message guiding users to run `pip install -e .`
   - Prevents confusing ModuleNotFoundError during test runs

2. **tests/test_constants.py** - Fixed dynamic imports
   - Changed `from cli import` to `from skill_seekers.cli import` (6 locations)
   - Fixes imports in test methods that dynamically import modules
   - All 16 tests now pass ✅

3. **tests/test_llms_txt_detector.py** - Fixed patch decorators
   - Changed `patch('cli.llms_txt_detector.` to `patch('skill_seekers.cli.llms_txt_detector.` (4 locations)
   - All 4 tests now pass ✅

4. **docs/CLAUDE.md** - Added "Running Tests" section
   - Clear instructions on installing package before testing
   - Explanation of why installation is required
   - Common pytest commands and options
   - Test coverage statistics

**Testing:**
- ✅ All 101 tests pass across the 7 affected files:
  - test_async_scraping.py (11 tests)
  - test_config_validation.py (26 tests)
  - test_constants.py (16 tests)
  - test_estimate_pages.py (8 tests)
  - test_integration.py (23 tests)
  - test_llms_txt_detector.py (4 tests)
  - test_llms_txt_downloader.py (13 tests)
- ✅ conftest.py check works correctly
- ✅ Helpful error shown when package not installed

**Impact:**
- Developers now get clear guidance when tests fail due to missing installation
- All test import issues resolved
- Better developer experience for contributors

tests/test_constants.py

@@ -109,14 +109,14 @@ class TestConstantsUsage(unittest.TestCase):
 
     def test_doc_scraper_imports_constants(self):
         """Test that doc_scraper imports and uses constants."""
-        from cli import doc_scraper
+        from skill_seekers.cli import doc_scraper
         # Check that doc_scraper can access the constants
         self.assertTrue(hasattr(doc_scraper, 'DEFAULT_RATE_LIMIT'))
         self.assertTrue(hasattr(doc_scraper, 'DEFAULT_MAX_PAGES'))
 
     def test_estimate_pages_imports_constants(self):
         """Test that estimate_pages imports and uses constants."""
-        from cli import estimate_pages
+        from skill_seekers.cli import estimate_pages
         # Verify function signature uses constants
         import inspect
         sig = inspect.signature(estimate_pages.estimate_pages)
@@ -125,7 +125,7 @@ class TestConstantsUsage(unittest.TestCase):
     def test_enhance_skill_imports_constants(self):
         """Test that enhance_skill imports constants."""
         try:
-            from cli import enhance_skill
+            from skill_seekers.cli import enhance_skill
             # Check module loads without errors
             self.assertIsNotNone(enhance_skill)
         except (ImportError, SystemExit) as e:
@@ -135,7 +135,7 @@ class TestConstantsUsage(unittest.TestCase):
 
     def test_enhance_skill_local_imports_constants(self):
         """Test that enhance_skill_local imports constants."""
-        from cli import enhance_skill_local
+        from skill_seekers.cli import enhance_skill_local
         self.assertIsNotNone(enhance_skill_local)
 
 
@@ -144,7 +144,7 @@ class TestConstantsExports(unittest.TestCase):
 
     def test_all_exports_exist(self):
         """Test that all items in __all__ exist."""
-        from cli import constants
+        from skill_seekers.cli import constants
         self.assertTrue(hasattr(constants, '__all__'))
         for name in constants.__all__:
             self.assertTrue(
@@ -154,7 +154,7 @@ class TestConstantsExports(unittest.TestCase):
 
     def test_all_exports_count(self):
         """Test that __all__ has expected number of exports."""
-        from cli import constants
+        from skill_seekers.cli import constants
         # We defined 18 constants (added DEFAULT_ASYNC_MODE)
         self.assertEqual(len(constants.__all__), 18)