feat: add local backend status probing and port availability checks i… #472

Job	Run time
Visualiser WASM (Go)	21s
Headless Self-Check (ubuntu-latest)	53s
E2E smoke	1m 29s
Lint	1m 27s
Frontend tests	3m 38s
Localization tests	1m 11s
Headless Self-Check (macos-latest)	1m 16s
Headless Self-Check (windows-latest)	3m 37s
Backend tests (Python 3.14) - Shard 1 / 4	5m 10s
Backend tests (Python 3.14) - Shard 0 / 4	4m 5s
Backend tests (Python 3.14) - Shard 3 / 4	4m 5s
Build frontend artifact / Build frontend artifact	57s
Backend tests (Python 3.14) - Shard 2 / 4	4m 44s
Native build (windows)	5m 37s
Linux build check	1m 32s
Native build (macos)	13m 42s
Validate Linux build artifact	14s
	53m 58s

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