Require opt-in for pipeline workspace tools

[chubes4]

Summary

• Move workspace policy tools off the synthetic pipeline_policy mode and onto real chat/pipeline modes.
• Mark write/git/worktree workspace tools with requires_opt_in so pipeline access remains explicit through allow-only policy.
• Update the workspace policy smoke to assert both real mode membership and opt-in metadata.

Related

• Depends on Support multi-mode AI runs data-machine#2022.
• Part of Multi-mode agent runs: kill pipeline_policy fake mode, replace inheritance hack with array agent_modes data-machine#2020.
• Follow-up World of WordPress PR will switch the world pipeline to additive agent_modes.

Validation

• php tests/smoke-workspace-policy-tools.php — OK, 31 assertions
• homeboy test data-machine-code — activation/install passed; PHPUnit discovery found zero tests

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the workspace tool registration update and smoke assertions, then ran validation; Chris remains responsible for review and merge.