feat: video pipeline OCR quality fixes + two-pass AI enhancement

- Skip OCR on WEBCAM/OTHER frames (eliminates ~64 junk results per video)
- Add _clean_ocr_line() to strip line numbers, IDE decorations, collapse markers
- Add _fix_intra_line_duplication() for multi-engine OCR overlap artifacts
- Add _is_likely_code() filter to prevent UI junk in reference code fences
- Add language detection to get_text_groups() via LanguageDetector
- Apply OCR cleaning in _assemble_structured_text() pipeline
- Add two-pass AI enhancement: Pass 1 cleans reference Code Timeline
  using transcript context, Pass 2 generates SKILL.md from cleaned refs
- Update video-tutorial.yaml prompts for pre-cleaned references
- Add 17 new tests (197 total video tests), 2540 tests passing

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

CLAUDE.md

@@ -290,7 +290,7 @@ pytest tests/test_mcp_fastmcp.py -v
 **Test Architecture:**
 - 46 test files covering all features
 - CI Matrix: Ubuntu + macOS, Python 3.10-3.13
-- **2,121 tests passing** (current v3.1.0), up from 700+ in v2.x
+- **2,540 tests passing** (current), up from 700+ in v2.x
 - Must run `pip install -e .` before tests (src/ layout requirement)
 - Tests include create command integration tests, CLI refactor E2E tests
 
@@ -808,7 +808,7 @@ pip install -e .
 
 Per user instructions in `~/.claude/CLAUDE.md`:
 - "never skip any test. always make sure all test pass"
-- All 2,121 tests must pass before commits (v3.1.0)
+- All 2,540 tests must pass before commits
 - Run full test suite: `pytest tests/ -v`
 - New tests added for create command and CLI refactor work