feat(connect): support explicit org selection in auth login

[lee-reinhardt]

Summary

Adds multi-org support to avocado connect auth login. Users who belong to more than one org can now choose which org their new CLI token will be scoped to, either via a --org flag for scripting or via an interactive picker.

What's new

• --org <id> flag scopes the new token to a specific org non-interactively. UUID-only, matching the convention in connect init and other org-scoped commands.
• Interactive terminal picker prompts when the flag is absent and the user belongs to multiple orgs. Same picker pattern as connect init so the UX feels consistent across the auth and project-setup flows.
• Single-org users see no change — the picker is skipped and the lone org is selected automatically.
• JSON output mode (--output json) with multiple orgs and no --org returns a clear error rather than hanging on a prompt the caller can't answer.

Mechanics

• Adds a new step between the browser callback and exchange: POST /auth/cli/list-orgs {code} returns the user's orgs and roles without consuming the one-time code (codes are stateless, so the same code is reused for the subsequent exchange call).
• POST /auth/cli/exchange now sends organization_id in the request body, letting the server scope the token at mint time.

Server dependency

Requires a server that supports the new list-orgs endpoint and the optional organization_id param on exchange. The corresponding server change is shipping ahead of any CLI release.

Tests

8 new unit tests cover the org-pick decision logic across every branch (zero/single/multi orgs, hint match/mismatch, JSON vs human output). The pure decision logic (pick_org) is split from the IO/UI (HTTP, stdin, stdout) so the tests target pure functions and run without a network or terminal.

Backwards compatibility

Older avocado binaries that don't send organization_id continue to work against the new server unchanged — the server preserves the existing scoping behavior for that case. Users opt into the picker by upgrading the CLI.

Draft status

Marked as draft pending the server-side change rolling out first, so CLIs that upgrade hit a server that already knows about the new endpoint.

[jasontwong]

LGTM — no blocking issues found.