fix: install scheduler from official Browser Use package

[MagMueller]

What changed

• replace the moving ShawnPana/browser-use@main Scheduler dependency with the official browser-use>=0.13.8 package
• import the callable sandbox decorator from browser_use.sandbox in both bundled agents

The package-only swap exposed a clean-room TypeError: module object is not callable: the root sandbox export resolves to the module in 0.13.8. The two explicit submodule imports are the matching fix. Scope is exactly three Scheduler files.

Verification

• both repository validators passed all 11 templates
• py_compile passed for Scheduler main and both agents
• clean isolated uv sync installed browser-use 0.13.8
• Agent, Browser, ChatBrowserUse, and callable browser_use.sandbox.sandbox imported
• Scheduler main, Gmail agent, and X agent imported without credentials
• git diff --check passed

---

Summary by cubic

Swaps the Scheduler's ShawnPana/browser-use@main git dependency for the official browser-use>=0.13.8 package. Because the root sandbox export in 0.13.8 is the module rather than the callable decorator, both bundled agents now import sandbox from browser_use.sandbox explicitly.

^{Written for commit fdccc5c. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}