Add braille renderer with amber demo GIF

- Braille canvas: 2×4 dots per cell (4× resolution vs half-blocks)
- Shared palettes, effects, and audio between both renderers
- README with both demos and build instructions for each

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

.gitignore

@@ -1,4 +1,6 @@
 /osc
+/osc_braille
+/osc_fast
 nimcache/
 demo.png/
 diag.png/