Add AuK voice-editing demo

Edits emotion on an existing recording in place (same speaker, words,
duration) rather than steering style at generation time. Demo runs
"Change the emotion to excited." on the public-domain narrator clip
already used by whisperx/tts.

Found and documented three real environment/packaging gaps on the RTX
3090: a missing audioread dependency, a huggingface_hub/transformers
version conflict from installing the hf CLI, and --cpu_offload being
mandatory (not optional) since AuK's own undoffloaded VRAM figures
exceed 24GB entirely. Also found the practical input-length ceiling is
~25-30s, not the several minutes a podcast episode would need — an 80s
clip OOM'd on attention memory even with offload enabled.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Y1oQ4h4WE4R9KRvMQLr5Ey

.gitignore

@@ -13,6 +13,7 @@ venv/
 *.safetensors
 models/
 weights/
+ckpts/
 
 # Audio I/O scratch
 *.wav
@@ -33,3 +34,6 @@ media-files/video/*.mp4
 # Compressed exports of demucs stems — keep committed for review without
 # local playback (the raw separated/*.wav stems stay local, per *.wav above)
 !demucs/*.mp3
+
+# Small public-domain demo evidence clip for the auk voice-editing demo
+!auk/*.wav