fix(security): update sandbox Pillow dependency

[0xjohnnydev]

What users see

The sandbox Python lock graph resolves Pillow 12.2.0, which GitHub Dependabot reports as vulnerable.

What changed

• Updated only libs/python/cua-sandbox/uv.lock to Pillow 12.3.0.
• This focused draft covers alerts fix: resize MCP screenshots to max 2000px #894 through fix(agent): Fix trajectory turn increment to keep agent decision and execution in same turn #899 and docs: add blog post on computer-use agent history #937 through fix(uitars): correct message ordering to prevent litellm serialization #943 for the sandbox lock graph.

Validation

• uv lock --check passed in libs/python/cua-sandbox.
• Confirmed the lockfile resolves Pillow 12.3.0.
• git diff --check passed.

Definition of Done

• Every visible sandbox Pillow alert is mapped to this focused draft.
• The sandbox lock graph resolves outside the reported vulnerable range.
• A maintainer reviews and advances this draft; this automation will not merge or mark it ready.

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This draft duplicates the same-surface sandbox draft #2727. Review #2727 instead; this PR is retained as a draft for traceability and will not be advanced by the automation.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[0xjohnnydev]

Closing this draft because #2727 already owns the same sandbox Pillow dependency change. Keeping both would duplicate review and create lockfile conflicts. No code was merged; please continue review on #2727.