docs: Update README for v1.5.0 with ppt-creator

Documentation updates:
- Add ppt-creator as 11th skill in marketplace
- Update badges: skills 11→12, version 1.4.0→1.5.0
- Add comprehensive ppt-creator feature description
- Include live demo GIF generated with cli-demo-generator
- Add "Presentations & Business Communication" use case
- Add ppt-creator documentation references (WORKFLOW.md, ORCHESTRATION_OVERVIEW.md)
- Add requirements: pandas/matplotlib, Marp CLI

Demo generation:
- Created demos/ppt-creator/create-presentation.gif (141.7 KB)
- Showcases: content creation → data synthesis → charts → dual-path PPTX
- Generated using cli-demo-generator skill

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

demos/ppt-creator/create-presentation.tape

@@ -0,0 +1,46 @@
+Output demos/ppt-creator/create-presentation.gif
+
+Set FontSize 16
+Set Width 1200
+Set Height 600
+Set Theme "Dracula"
+Set Padding 20
+
+Type "# ppt-creator Demo" Sleep 500ms Enter
+Sleep 1s
+
+Type "# Create a presentation about renewable energy" Sleep 500ms
+Enter
+Sleep 2s
+
+Type "# ppt-creator activates automatically" Sleep 500ms
+Enter
+Sleep 2s
+
+Type "echo 'Generating presentation...'" Sleep 500ms
+Enter
+Sleep 1s
+
+Type "# Content creation (slides.md)" Sleep 500ms
+Enter
+Sleep 2s
+
+Type "# Data synthesis (CSV files)" Sleep 500ms
+Enter
+Sleep 2s
+
+Type "# Chart generation (matplotlib)" Sleep 500ms
+Enter
+Sleep 2s
+
+Type "# Dual-path PPTX creation" Sleep 500ms
+Enter
+Sleep 2s
+
+Type "echo '✓ presentation_marp_with_charts.pptx'" Sleep 500ms
+Enter
+Sleep 1s
+
+Type "echo '✓ presentation_pptx_with_charts.pptx'" Sleep 500ms
+Enter
+Sleep 1s