feat: add sandbox pool claim support

[sfroment]

How this was generated

1. Vendored client (koyeb/api*, spec/openapi.json)

# regenerate sync + async clients via openapi-generator (docker), then apply patches
OPENAPI_GENERATOR_VERSION=v7.24.0 make gen-api-client

make gen-api-client runs:

• gen-api-client-sync / gen-api-client-async — openapi-generator-cli generate over spec/openapi.json → koyeb/api/ and koyeb/api_async/
• ./scripts/apply_patches.sh — applies patches/002-api-client-fixes.patch

The old patches/001-proxy-support.patch was absorbed upstream in openapi-generator v7.24.0, so its file is dropped and apply_patches.sh updated.

2. Generated API docs (docs/api.md, docs/api_async.md)

# scripts/generate_docs.sh — pydoc-markdown over the regenerated client
uv run --frozen pydoc-markdown -p koyeb/api       > docs/api.md
uv run --frozen pydoc-markdown -p koyeb/api_async > docs/api_async.md

3. Build fix

Makefile test: target was python -m unitest (typo, and unittest wouldn't run the pytest suite anyway) → uv run pytest.

---

~29K of the diff is generated churn (openapi-generator re-emits ~320 model files; spec/openapi.json is 18K lines re-serialized). No hand-written code in this PR — that's #64.