Switch the zizmor check to fail on any finding at medium severity or
above (advanced-security off, min-severity medium, annotations on) so it
can be promoted to a required check, and pin the engine to zizmor 1.24.1
through zizmor-action v0.5.6 for deterministic runs.
Clear the findings that were outstanding so the check passes: correct
mismatched action pin version comments, scope the proxy endpoint
workflow's id-token and pull-requests permissions to the jobs that use
them, and mark the server-root-path docker build as non-publishing while
dropping its shared gha build cache.
* chore(ci): remove Agent Shin pull_request_target workflows
Drop the two Agent Shin workflows that ran on the pull_request_target
trigger: the PR triage workflow and the review gate. Both were dry-run
and gated behind AGENT_SHIN_ENABLED, so no live automation changes.
The shared scripts under .github/scripts stay in place; four other
Agent Shin workflows still depend on them and run on schedule, dispatch,
and issue events rather than pull_request_target
* ci(zizmor): also run on litellm_internal_staging
