v7: standalone Sing Detect app — full Tauri project tree

Promotes the v6 detection slice into a complete, buildable Tauri 2 app and
renames Stream Studio → Sing Detect (detection-only; video-concat split to its
own project). Proper src/ + src-tauri/ layout, Python sidecar under sidecar/,
app icons, package/Cargo manifests, and dev/build/pack scripts.

Pipeline unchanged in spirit: Rust drives ffmpeg to a 16 kHz mono WAV, the
Python sidecar (inaSpeechSegmenter) emits line-JSON segments, and Rust writes
EDL / markers CSV / CSV / JSON exports. Long ops run on spawn_blocking; cancel
kills the whole py -3.10 process tree.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -1,7 +1,40 @@
+# deps & caches
+node_modules/
 __pycache__/
 *.pyc
-*.wav
-*.mp4
-.DS_Store
-venv/
 .venv/
+venv/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+# build outputs
+target/
+dist/
+dist-portable/
+build/
+# logs & databases
+*.log
+*.db
+*.sqlite
+*.sqlite3
+# secrets / credentials
+.env
+*.env
+*cookie*
+*credential*
+credentials.json
+token.json
+*token.json
+.cookies.json
+google_cred/
+*.pem
+*.key
+# model weights / large artifacts
+*.onnx
+*.pt
+*.pth
+*.ckpt
+*.safetensors
+# os cruft
+.DS_Store
+Thumbs.db