Add agent analytics commands over /v1/analytics/*

[ellipsis-dev]

Adds an agent analytics command group so agents (and humans) can query the org's GitHub PR + review analytics — the data behind the /analytics dashboard — from the terminal.

Requested by @hbrooks in Slack. Backend PR (adds the token-auth /v1/analytics/* endpoints): ellipsis-dev/ellipsis#5625 — merge that first.

Commands

agent analytics reviewers --account-type bot   # which apps review the most PRs
agent analytics reviewers --sort comments -l 5 --repo owner/name
agent analytics prs --days 30                  # PR volume + human/bot split
agent analytics reviews --repo my-service      # review totals + top reviewers

• All subcommands take --days N (server default: last 30 days) or --start/--end, and --json for the raw API response (agent/script friendly).
• reviewers reads the reviewers leaderboard from GET /v1/analytics/metrics (--account-type, --repo owner/name, --sort reviews|approved|changes-requested|comments|lines, --limit).
• prs wraps GET /v1/analytics/pull-requests (maps --account-type user|bot to the endpoint's raw User/Bot filter; --status repeatable).
• reviews wraps GET /v1/analytics/reviews (--repo bare name, --author reviewer login, --review-state, top-reviewers table from the facets).

Also: typed mirrors of the three response models in src/lib/types.ts, three ApiClient methods, README usage block.

Verification

• npm run typecheck and npm run build green.
• --help output smoke-checked for the group and each subcommand from the built bundle.