review: add 'agent review default' to set the default code review pipeline

[ellipsis-dev]

Companion to ellipsis-dev/ellipsis#6032 (the backend half — merge that first). Requested by @hbrooks (Slack): a way to programmatically set the default code review config.

What

agent review default — which code review pipeline runs when an explicit review (agent review … / POST /v1/reviews) names none. A two-rung ladder mirroring agent config default, with the same --repo semantics (absent → account rung; bare --repo → the repo you're standing in; --repo owner/name → that repo):

agent review default                     # the effective default where you stand
agent review default list                # every rung, with broken-pointer badges
agent review default set crcfg_… [-r]    # point the account or a repo rung
agent review default clear [-r]          # clear a rung

Only explicit reviews read the ladder — webhook reviews keep matching the pipelines' own pull_requests: filters.

• src/commands/review.ts — the default group (bare show / list / set / clear).
• src/lib/api.ts + src/lib/types.ts — listReviewDefaults / putReviewDefault / deleteReviewDefault over GET/PUT/DELETE /v1/reviews/defaults, hand-rolled types like the /v1/defaults trio (neither is in the SDK's OpenAPI allowlist).
• src/commands/config.ts — exports resolveRepoFlag so both ladders share the --repo semantics.

Testing

• New ApiClient review defaults block in test/api.test.ts (paths, methods, envelope unwrap, the repository query param encoding).
• npm run typecheck clean; npm test 389 passed.
• Smoke-tested agent review default --help / agent review --help rendering via tsx.

🤖 Generated with Claude Code