opencodezen4dsh v0.4.0-fork.5

Fixes the Zen free-tier 403 FreeTierError on derived sessions and makes
every build self-describing.

Changes

Timestamp-valid ses_ / msg_ ids generated like the opencode CLI
(tU()), cached per conversation so prompt-cache affinity stays stable.
CLI-identical headers: User-Agent: opencode/1.18.31,
x-opencode-project: global, x-opencode-request: msg_…; no
x-session-affinity / X-Session-Id. anthropic-version stays on the
anthropic route (fork.4).
Version stamp: lib/version.json in the tarball; the release workflow
fails when the tag and package.json disagree and publishes a .sha256
sidecar next to the tarball.

dsh plugin --profile web add ./opencodezen4dsh-dsh-plugin-0.4.0-fork.5.tgz

Verify with sha256sum -c opencodezen4dsh-dsh-plugin-0.4.0-fork.5.tgz.sha256.