fix: remove arbitrary limits, fix hardcoded languages, and fix summarizer bugs

Stage 1 quality improvements from the Arbitrary Limits & Dead Code audit:

Reference file truncation removed:
- codebase_scraper.py: remove code[:500] truncation at 5 locations — reference
  files now contain complete code blocks for copy-paste usability
- unified_skill_builder.py: remove issues[:20], releases[:10], body[:500],
  and code_snippet[:300] caps in reference files — full content preserved

Enhancement summarizer rewrite:
- enhance_skill_local.py: replace arbitrary [:5] code block cap with
  character-budget approach using target_ratio * content_chars
- Fix intro boundary bug: track code block state so intro never ends
  inside a code block, which was desynchronizing the parser
- Remove dead _target_lines variable (assigned but never used)
- Heading chunks now also respect the character budget

Hardcoded language fixes:
- unified_skill_builder.py: test examples use ex["language"] instead of
  always "python" for syntax highlighting
- how_to_guide_builder.py: add language field to HowToGuide dataclass,
  set from workflow at creation, used in AI enhancement prompt

Test fixes:
- test_enhance_skill_local.py: rename test to test_code_blocks_not_arbitrarily_capped,
  fix assertion to count actual blocks (```count // 2), use target_ratio=0.9

Documentation:
- Add Stage 1 plan, implementation summary, review, and corrected docs
- Update CHANGELOG.md with all changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_enhance_skill_local.py

@@ -356,14 +356,17 @@ class TestSummarizeReference:
         # Result should be significantly shorter than original
         assert len(result) < len(content)
 
-    def test_code_blocks_capped_at_five(self, tmp_path):
+    def test_code_blocks_not_arbitrarily_capped(self, tmp_path):
+        """Code blocks should not be arbitrarily capped at 5 - should use token budget."""
         enhancer = self._enhancer(tmp_path)
-        content = "\n".join(["Intro line"] * 20) + "\n"
+        content = "\n".join(["Intro line"] * 10) + "\n"  # Shorter intro
         for i in range(10):
-            content += f"```python\ncode_block_{i}()\n```\n"
-        result = enhancer.summarize_reference(content)
-        # Should have at most 5 code blocks
-        assert result.count("```python") <= 5
+            content += f"```\ncode_block_{i}()\n```\n"  # Short code blocks
+        # Use high ratio to ensure budget fits well beyond 5 blocks
+        result = enhancer.summarize_reference(content, target_ratio=0.9)
+        # Each block has opening + closing ```, so divide by 2 for actual block count
+        code_block_count = result.count("```") // 2
+        assert code_block_count > 5, f"Expected >5 code blocks, got {code_block_count}"
 
 
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