perf(workers): compress negotiated workspace manifests (#142242)

perf(workers): compress negotiated workspace manifests (#142242)

Negotiate bounded gzip for workspace manifests and share HTTP decoding with existing callers. Preserve authorization, cancellation and decoded-size limits while retaining identity transfers for other clients.

Current-source 235 tests, full changed checks and docs validation pass. Real authenticated HTTP proof sends the identical 12000-file manifest in 548761 bytes rather than 1755103, a 68.73 percent reduction. Existing independent review applies to the unchanged implementation; documentation follows the current session-lifecycle page.