- Fix FDK-AAC C shim: use proper OUT_BITSTREAM_DATA=3 constant and INT types
- Add frame-aligned PCM accumulation buffer to AAC encoder for clean output
- Add fdkaac_encode and fdkaac_close to C shim (all FDK-AAC calls in C)
- Implement crossfade between tracks (3s overlap, 2s fade-in/out)
- Tune buffer: 90% drain sleep for encoding headroom, 64KB burst-on-connect
- Add FFI bindings for new shim functions
- Rewrite README.org with full architecture docs and integration plan