This PR updates the Opencode scenario-suite flow so CLI agents can still use file and bash tools, but only inside a clean per-scenario workspace.

Changes include:

• Stage each Opencode benchmark run into an isolated workspace outside the repo.
• Copy only allowed scenario inputs into the workspace:question.txt, manifest.json, manifest-referenced data files
• Exclude benchmark-only artifacts such as: groundtruth.txt, reports/, traces/, previous outputs
• Run Opencode from the staged workspace instead of the repository root.
• Hide benchmark artifact paths from the Opencode subprocess environment.
• Reject unsafe workspace roots inside the repo when file/bash/edit tools are enabled.
• Add tests for workspace staging and unsafe workspace validation.