feat(tickets): support explicit batch creation

[BjRo]

Why

Closes #222. The ticket skill previously capped one invocation at one ticket, even when the caller explicitly requested a finite set of distinct tickets.

What changed

The darrow-tickets skill now processes each explicitly named item in order: classify it, search for duplicates, draft and create it, read back caller-named relations, and report its outcome. A backend or relation failure stops later creations while preserving completed effects; singular requests still create at most one ticket. The specification, plugin guidance, stateful GitHub eval fixture, and colocated evals cover these boundaries. The plugin version is 0.6.0 on both hosts. The read-ticket description now puts the explicit provider boundary first, and its evals accept the CLI's valid --provider github flag.

Verification

• Native evals: all four case groups (create-ticket-, read-ticket-, list-tickets-, update-ticket-) passed with --trials 1 --jobs 1 on both --harness codex and --harness claude (33/33 per host). The explicit batch case also passed three consecutive Claude trials; independent static review verified the final duplicate-search and relation-readback assertions.
• Passed: bun run check:python (including 162 darrow-tickets tests), bun run check:docs, bun run lint, bun run lint:ts, bun run lint:shell, bun run typecheck, bun run check:decisions, bun run eval:coverage (valid), and git diff --check.
• bun test: 621 passed, 20 failed in review-outcome-eval-checks.test.ts and review-route-eval-checks.test.ts. Both affected files reproduce the same 20 failures on the original main checkout. Bash script tests are not applicable; no Bash scripts changed.

Review notes

Focus on the per-item search/create/readback order and the report after a partial relation failure. The CLI still creates one issue per create command; the skill coordinates the caller-authorized batch. No runtime migration is required.

Checklist

• I have read and followed CONTRIBUTING.md, including the contribution
  licensing terms.
• I added or updated the applicable invariant before implementation, or
  this change does not affect a capability invariant.
• I added or updated colocated evals, or this change does not affect skill
  behavior.
• I confirmed that each changed plugin remains self-contained, or this
  change does not affect plugin content.
• I ran bun run check:python, or this change does not affect registered
  Python packages or their repository quality infrastructure.