feat(sandboxes): add typed image listing

[akirillo]

The VM sandbox load-test bootstrap and the Prime CLI need one typed path for image discovery. Previously, the lightweight SDK did not expose GET /images, and prime images list duplicated the endpoint's query and response handling with untyped dictionaries.

This change adds synchronous and asynchronous SDK listing with typed artifact rows, pagination, build status, artifact type, owner type, and existing visibility values. The models mirror the platform FastAPI ImageResponse and GenericPaginationResponse schemas. They preserve camel-case API aliases while accepting the backend's current snake-case pagination key and legacy responses that omit the total count. Listing follows configured team context, supports platform scope, validates pagination, and rejects conflicting platform and team scopes.

prime images list now delegates request construction and parsing to ImageClient.list, renders directly from the typed models, and emits camel-case JSON. The CLI dependency floor is prime-sandboxes>=0.2.39, the planned release containing this API. No package version changes are included.

Test: Ruff and type checks pass. All 87 focused SDK and CLI image-list tests pass. The 197 hermetic sandbox SDK tests also pass. Live sync, async, and CLI personal listings parsed successfully; the supplied non-admin key received 403 Admin role required for platform scope, so a successful platform response remains unverified.

[chatgpt-codex-connector]

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