feat: replace all emojis on demo page with SVG icons

Define a JS SVG icon library (music, branch, merge, conflict, revert, check, dot, zap, pause, eye) and use it throughout:

- ACT_ICONS: 🎵🌿⚡🔀⏪ → music/branch/merge/conflict/revert SVGs - Dimension tooltip pills: ● → dot SVG, ⚡ → zap SVG - Event log conflict dim-pills: ⚡ → zap SVG - Dimension matrix cells: textContent ⚡/● → innerHTML zap/dot SVG - Play button: ⏸/✓ → pause/check SVGs (textContent → innerHTML) - Reveal All button: ✦ → eye SVG (textContent → innerHTML) - HTML conflict note: ⚡ → alert-triangle SVG, ✓ → check SVG

Add .ico-inline, .ico-conflict, .ico-check CSS for the static HTML icons.