[cli] Move openapi urls to /openapi

Nobody has claimed this yet.

as discussed in #774

My proposed change is something like this:

| api | previous | new | proposed |
|---|---|---|---|
| foundry | /openai/status | /status | foundry/v1/status |
| foundry | | /shutdown | foundry/v1/shutdown |
| foundry | /openai/loadedmodels | /models/loaded | foundry/v1/models/loaded |
| foundry | /openai/load/{name} | /models/load/{name} | foundry/v1/models/load/{name} |
| foundry | /openai/unload/{name} | /models/unload/{name} | foundry/v1/models/unload/{name} |
| openai | | /v1/models | openai/v1/models |
| openai | | /v1/models/{name} | openai/v1/models/{name} |
| openai | /v1/chat/completions | /v1/chat/completions | openai/v1/chat/completions |
| openai | /v1/audio/transcriptions | /v1/audio/transcriptions | openai/v1/audio/transcriptions |
| openai | | /v1/embeddings | openai/v1/embeddings |
| openai | | /v1/responses | openai/v1/responses |
| openai | | /v1/responses/{id} | openai/v1/responses/{id} |
| openai | | /v1/responses/{id}/input_items | openai/v1/responses/{id}/input_items |

When using an openai compatible client you would then use `http://localhost:xxxx/openapi/v1` as the base url
This also leaves a path for non-breaking upgrades to foundry api, and adding other rest apis like ollama or anthropic.

No source files or tests are named. Start by locating the CLI's OpenAPI route registration and the endpoint tests, then compare the current paths with the proposed table. Done means the routes use the /openapi/{api}/v1 structure, including foundry and openai endpoints, while the compatible client base URL works as described.

Written by the indexing model from the issue text.