Add `sift batch` so agents reach the batch endpoint through the CLI like
`fetch` and `search`. `batchcmd.go` has `parseBatchArgs` (verb plus the
unchanged args after it; submit takes one arg, status a job id optionally
preceded by `--results`, get a job id plus a non-negative-integer idx, cancel
a job id, else a usage error), `batchMain` dispatch, one small function per
verb, and `batchDo` (bearer header, decode the envelope, print it on stdout,
on non-2xx the error to stderr and `exitFor`). `submitMain` reads the file or
stdin and validates locally: a JSON object with a non-empty `targets` array,
or a bare array of targets or URL strings wrapped into `{"targets": [...]}`.
README gains a "Batch" section (endpoints, serial-per-job/one-worker/
round-robin model, caps, idempotency, lease/TTL/restart, summary-vs-results,
redaction, metrics); SKILL.md gains a "Batch" section.
Co-Authored-By: ornith-1.5-35b-a3b <ornith-1.5-35b-a3b@llama.cpp.invalid>
kyleandornith-1.5-35b-a3b
be48ecb550