Extract common CSS to 5 external stylesheets (DRY)

- base.css: Core layout, typography, container
- nav.css: Navigation bar styles
- forms.css: Form elements, buttons, inputs, checkboxes
- quests.css: CSS-only easter eggs
- results.css: Media grid and result card styles

Templates now link external CSS via extra_css_links block.
Page-specific styles remain inline (correct pattern).
Fixed OVER_9000 test (it's OVER 9000, so 9001).

tests/unit/test_database.py

@@ -44,8 +44,8 @@ class TestScoreConstants:
         assert SCORE_FULL_RES == 10
 
     def test_over_9000(self):
-        """Test the limit constant."""
-        assert OVER_9000 == 9000
+        """Test the limit constant - it's OVER 9000!"""
+        assert OVER_9000 == 9001
 
 
 class TestDatabaseInitialization: