feat: optimize skills + add pipeline handoff chaining across 9 skills

asr-transcribe-to-text:
- Add local MLX transcription path (macOS Apple Silicon, 15-27x realtime)
- Add bundled script transcribe_local_mlx.py with max_tokens=200000
- Add local_mlx_guide.md with benchmarks and truncation trap docs
- Auto-detect platform and recommend local vs remote mode
- Fix audio extraction format (MP3 → WAV 16kHz mono PCM)
- Add Step 5: recommend transcript-fixer after transcription

transcript-fixer:
- Optimize SKILL.md from 289 → 153 lines (best practices compliance)
- Move FALSE_POSITIVE_RISKS (40 lines) to references/false_positive_guide.md
- Move Example Session to references/example_session.md
- Improve description for better triggering (226 → 580 chars)
- Add handoff to meeting-minutes-taker

skill-creator:
- Add "Pipeline Handoff" pattern to Skill Writing Guide
- Add pipeline check reminder in Step 4 (Edit the Skill)

Pipeline handoffs added to 8 skills forming 6 chains:
- youtube-downloader → asr-transcribe-to-text → transcript-fixer → meeting-minutes-taker → pdf/ppt-creator
- deep-research → fact-checker → pdf/ppt-creator
- doc-to-markdown → docs-cleaner / fact-checker
- claude-code-history-files-finder → continue-claude-work

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

transcript-fixer/references/example_session.md

@@ -0,0 +1,25 @@
+# Example Session
+
+## Input transcript (`meeting.md`)
+```
+今天我们讨论了巨升智能的最新进展。
+股价系统需要优化，目前性能不够好。
+```
+
+## After Stage 1 (`meeting_stage1.md`)
+```
+今天我们讨论了具身智能的最新进展。  ← "巨升"→"具身" corrected
+股价系统需要优化，目前性能不够好。  ← Unchanged (not in dictionary)
+```
+
+## After Stage 2 (`meeting_stage2.md`)
+```
+今天我们讨论了具身智能的最新进展。
+框架系统需要优化，目前性能不够好。  ← "股价"→"框架" corrected by AI
+```
+
+## Learned pattern detected
+```
+✓ Detected: "股价" → "框架" (confidence: 85%, count: 1)
+  Run --review-learned after 2 more occurrences to approve
+```