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>

dev.bat

@@ -0,0 +1,13 @@
+@echo off
+REM Sing Detect - run in development (hot-reload UI + Rust).
+REM Requires: Node, Rust (cargo), ffmpeg on PATH.
+setlocal
+set "PATH=%USERPROFILE%\.cargo\bin;%PATH%"
+
+if not exist "node_modules" (
+  echo Installing npm dependencies...
+  call npm install
+)
+
+echo Starting Sing Detect (dev)...
+call npm run tauri dev