cli: add `entire api` authenticated passthrough (core + cell)

A gh api-style escape hatch: make an authenticated request to an Entire API and print the JSON response, with the CLI attaching the right bearer and dialing the right host.

entire api /api/v1/clusters # control plane entire api --to cell /api/v1/me/activity # home entire-api cell entire api --to cell "/api/v1/me/recap?repo={repo_id}"

• --to core (default) reuses the same bearer resolution as auth token (honors ENTIRE_TOKEN, else the active context); --to cell mints the jurisdictional token via NewEntireAPICellClient. Data API is omitted deliberately — it's being retired.
• Placeholders filled from the origin remote: {owner}, {repo}, and {repo_id} (the repo's ULID, resolved from its mirror) — the last is what cell endpoints key on.
• Method defaults to GET, or POST when -f/-F fields or --input is given; -X overrides. GET + fields go on the query string. -H adds headers, -i prints status + headers, and JSON responses are pretty-printed.
• Adds api.Client.Request as the general method/header escape hatch behind it.