fix(cli): decode caches list as bare array (#290)

[DerDennisOP]

Summary

• gradient cache list printed api error (200): {...} instead of formatting the cache list.
• Root cause: GET /caches returns message as a bare array (server, docs, and frontend all agree), but the CLI connector's caches().list() decoded Paginated<Vec<ListItem>> — a copy of the orgs/projects pattern. The shape mismatch made decode<T> fail to parse the envelope and fall through to the raw-body error path, rendering a successful 200 as an api error.
• Fix: caches().list() now returns ListResponse (Vec<ListItem>), matching the documented ListResponse contract; the cache list command iterates the Vec directly (mirroring orgs subscriptions).

No server, API-doc, or frontend changes needed — they already use the bare-array contract; only the connector was the outlier.

Fixes #290

Test plan

• cargo test -p connector --test caches_api — list_caches_decodes_bare_array replays the exact response from the bug report and asserts it decodes into a Vec.
• Manual: gradient cache list against a server with at least one cache prints name: id lines instead of an api error (200).