feat: add interactive CNN browser demo for GitHub Pages (#253)

- Single-file HTML demo with modern dark theme UI
- Drag & drop image upload + camera capture
- Real-time embedding extraction and visualization
- Similarity matrix comparing multiple images
- Performance metrics display (~5ms per image)
- Falls back to demo mode if WASM fails to load
- ADR-089 documenting the approach

Deploy to: https://ruvnet.github.io/ruvector/demo/cnn/

Co-authored-by: Reuven <cohen@ruv-mac-mini.local>

docs/adr/ADR-089-cnn-browser-demo.md

@@ -0,0 +1,44 @@
+# ADR-089: CNN Browser Demo for GitHub Pages
+
+## Status
+Accepted
+
+## Context
+The `@ruvector/cnn` npm package provides WASM-based CNN feature extraction for browsers. To showcase its capabilities and provide a hands-on experience, we need an interactive demo deployable to GitHub Pages.
+
+## Decision
+Create an interactive browser demo with:
+
+### Features
+1. **Image Upload** - Drag & drop or file picker
+2. **Camera Capture** - Real-time webcam integration
+3. **Feature Extraction** - Visual display of embedding vectors
+4. **Similarity Search** - Compare images and show similarity scores
+5. **Live Heatmap** - Feature activation visualization
+6. **Performance Metrics** - Real-time latency display
+
+### Technical Approach
+- Single HTML file with embedded CSS/JS for easy deployment
+- ES modules loading WASM directly from npm CDN (unpkg/jsdelivr)
+- Canvas-based visualizations
+- No build step required
+
+### Deployment
+- GitHub Pages via `docs/demo/cnn/` directory
+- Direct URL: `https://ruvnet.github.io/ruvector/demo/cnn/`
+
+## Consequences
+
+### Positive
+- Zero-install demo experience
+- Showcases real WASM performance (~5ms/image)
+- Educational tool for understanding embeddings
+- Marketing asset for the package
+
+### Negative
+- CDN dependency for WASM module
+- Browser compatibility limited to WASM-supporting browsers
+
+## Implementation
+- `docs/demo/cnn/index.html` - Main demo page
+- Uses `@ruvector/cnn` from unpkg CDN