[nicoloboschi]

Fixes #5709.

Problem: uv sync --frozen --python 3.14 --package hindsight-api-slim fails. The lock pins onnxruntime 1.20.1 on every platform, and that version has no cp314 wheels. The cap comes from magika 0.6.x (pinned by every markitdown release), which limits onnxruntime to <=1.20.1 on win32 only. The universal lock applied it everywhere.

Fix:

• Root pyproject.toml: constraint-dependencies = ["onnxruntime>=1.24.1; sys_platform != 'win32'"], so uv forks onnxruntime by platform. Windows keeps 1.20.1, every other platform gets 1.31.0.
• asyncpg 0.30.0 → 0.31.0, the first release with cp314 wheels. Not 0.32.0, which changes pool min_size behaviour.
• onnxruntime 1.31 ships type hints, so the embeddings code wraps the session output in np.asarray, as the cross-encoder already does.
• CI: build-api-python-versions only installed with a fresh resolve, so it never read the lock. It now also installs from uv.lock on 3.11–3.14 and imports onnxruntime, magika, markitdown and asyncpg.

What else changes: Linux, macOS and Docker installs from the lock now run onnxruntime 1.31.0 (was 1.20.1) and asyncpg 0.31.0 (was 0.30.0).

Tested:

• The frozen sync fails on the old lock and works on the new one, on 3.14 and on 3.12. The imports work on both.
• ONNX embedding, reranker and runtime tests, markitdown tests, file retain tests and DB pool tests: 85 passed, 3 skipped, 0 failed.
• lint.sh passes.
• Not tested on Windows.