fix(review): restore the judge's 20m effective bound + stale help (trail findings)

Trail findings on this branch caught two regressions the reviews missed:

• The judge's effective no-flag bound silently dropped 20m -> 5m: on main the --timeout flag default (20m) always flowed into SynthesisSink.ProviderTimeout, so the 5m defaultSynthesisProviderTimeout was nearly dead code on this path; with the flag default now 0, the 5m fallback became live and tightened the judge 4x — against this PR's own thesis, and a judge timeout discards the whole multi-reviewer run with no verdict. The synthesis default is now 20m, preserving the prior effective bound while keeping the judge always bounded.

• The command's Long help still promised 'default 20m; 0 disables both bounds' — both claims stale. Rewritten to the new contract: no reviewer default, judge separately bounded and never uncapped.