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>

src/skill_seekers/cli/codebase_scraper.py

@@ -419,7 +419,7 @@ def extract_markdown_structure(content: str) -> dict[str, Any]:
             structure["code_blocks"].append(
                 {
                     "language": language,
-                    "code": code[:500],  # Truncate long code blocks
+                    "code": code,  # Full code - no truncation
                     "full_length": len(code),
                 }
             )
@@ -486,7 +486,7 @@ def extract_rst_structure(content: str) -> dict[str, Any]:
                 "code_blocks": [
                     {
                         "language": cb.language or "text",
-                        "code": cb.code[:500] if len(cb.code) > 500 else cb.code,
+                        "code": cb.code,  # Full code - no truncation
                         "full_length": len(cb.code),
                         "quality_score": cb.quality_score,
                     }
@@ -572,7 +572,7 @@ def extract_rst_structure(content: str) -> dict[str, Any]:
             structure["code_blocks"].append(
                 {
                     "language": language,
-                    "code": code[:500],
+                    "code": code,  # Full code - no truncation
                     "full_length": len(code),
                 }
             )
@@ -717,7 +717,7 @@ def process_markdown_docs(
                                     for h in parsed_doc.headings
                                 ],
                                 "code_blocks": [
-                                    {"language": cb.language, "code": cb.code[:500]}
+                                    {"language": cb.language, "code": cb.code}  # Full code
                                     for cb in parsed_doc.code_blocks
                                 ],
                                 "tables": len(parsed_doc.tables),
@@ -743,7 +743,7 @@ def process_markdown_docs(
                                     for h in parsed_doc.headings
                                 ],
                                 "code_blocks": [
-                                    {"language": cb.language, "code": cb.code[:500]}
+                                    {"language": cb.language, "code": cb.code}  # Full code
                                     for cb in parsed_doc.code_blocks
                                 ],
                                 "tables": len(parsed_doc.tables),