Fix sidecar not found on Windows/macOS/Linux: switch from externalBin to resources

Tauri's externalBin only bundled the single sidecar executable, but
PyInstaller's onedir output requires companion DLLs and _internal/.
The binary was also renamed with a target triple suffix that
resolve_sidecar_path() didn't look for, causing it to fall back to
dev mode which used a compile-time CI path (CARGO_MANIFEST_DIR).

- Switch from externalBin to bundle.resources to include all sidecar files
- Pass Tauri resource_dir to sidecar manager for platform-aware path resolution
- Remove rename_binary() since externalBin target triple naming is no longer needed
- Remove broken production-to-dev fallback that could never work on user machines

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

python/build_sidecar.py

@@ -236,10 +236,9 @@ def main() -> None:
     python = create_venv_and_install(cpu_only)
     output_dir = run_pyinstaller(python)
     download_ffmpeg(output_dir)
-    rename_binary(output_dir, target_triple)
 
     print(f"\n[build] Done! Sidecar built at: {output_dir}")
-    print(f"[build] Copy contents to src-tauri/binaries/ for Tauri bundling")
+    print(f"[build] Copy directory to src-tauri/sidecar/ for Tauri resource bundling")
 
 
 if __name__ == "__main__":