feat: [rttp] Emit HTTP/2 response trailers from the prior-knowledge server path

[fewensa]

Adds HTTP/2 prior-knowledge response trailer emission and matching client trailer decoding, with focused h2 integration coverage and full workspace verification.

Metadata

version: 1
issue: https://plane.kahub.in/endless/browse/HBX-1376/
work_kind: code_work
branch: hbx-1376-rttp-emit-http-2-response
base: main
commit: 0c60dd577e9b107b31723f31998bd160d27d110e
source_references:
  - kind: plane_issue
    canonical: https://plane.kahub.in/endless/browse/HBX-1376/
    url: https://plane.kahub.in/endless/browse/HBX-1376/
    close_policy: link_only

[chatgpt-codex-connector]

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