feat(engine): make AddNode non-blocking with async node creation #1035

Job	Run time
Skit / Build	7m 18s
UI / Knip (unused code)	14s
UI / Build	19s
E2E / Playwright E2E	7m 17s
UI / Lint (TypeScript + ESLint)	38s
UI / Test	30s
Skit / Test	6m 6s
Skit / Lint (fmt + clippy)	3m 32s
Plugins / Lint (Simple Plugins)	1m 4s
Plugins / Lint (NLLB)	2m 12s
Plugins / Lint (Sherpa-ONNX Plugins)	1m 1s
Skit / Test (GPU)	1m 51s
Plugins / Lint (Whisper)	46s
Plugins / Format Check	16s
All Checks Passed	1s
	33m 5s

Provide feedback