feat(infra): build the durable queue and isolated scan worker

[back1ash]

Summary

Execute the same pinned core used by the CLI inside a bounded, no-egress hosted worker.

Scope

• Consume immutable content-addressed scan inputs from a durable queue.
• Run with no network, read-only inputs, bounded CPU, memory, wall time, output, and process count.
• Keep GitHub installation credentials outside the worker.
• Persist normalized terminal results and provenance atomically.
• Support bounded retry without changing normalized analysis identity.

Acceptance criteria

• Untrusted repository content is treated only as data.
• Timeout, resource exhaustion, protocol failure, and crash become visible internal-error results.
• A successful worker result matches local CLI normalized bytes for the same inputs.
• Retry does not duplicate terminal artifacts or overwrite earlier attempts.
• No network request is possible from the analysis process.

Dependencies

• docs(security): define the initial threat model #8
• feat(github): verify webhooks and persist idempotent scan requests #30
• feat(github): fetch trusted PR snapshots and effective policy #32
• build(release): package the CLI with SBOM and provenance #28

Priority gate and claiming

Keep status:blocked until every open priority:p1 issue is closed,
the Phase 0 hosted-product decision is proceed, and every explicit
dependency above is closed. Only then replace it with status:ready
and add help wanted.

To claim a ready issue, assign yourself, replace status:ready with
status:in-progress, and comment with a short implementation plan.

Non-goals

• GitHub token use, report rendering, or arbitrary customer code execution.
• General-purpose CI workloads.