fix: propagate tools.startup-timeout to gateway.startupTimeout (prevents safeoutputs eviction on slow runners) (#46875)

* Initial plan

* fix: propagate tools.startup-timeout to gateway.startupTimeout to prevent safeoutputs timeout

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* docs(adr): add draft ADR-46875 for always emitting gateway.startupTimeout

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

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 4 people