Let safehouse agents use mcporter's vault

[technicalpickles]

Summary

• Scripts that talk to MCP servers through mcporter died under safe with EPERM on ~/.mcporter, which is where mcporter keeps its OAuth vault, schema caches and locks. common.sb now grants it read/write.
• mcporter.json and mcporter.jsonc stay write-denied. They name stdio server commands, so a sandboxed agent that could edit them could get code run unsandboxed the next time mcporter runs outside.
• ADR 0060's list of what common.sb covers picks up the new grant.

Test plan

Ran safehouse directly with this branch's common.sb and role-work.sb: reading credentials.json and writing a scratch file in ~/.mcporter work, writing mcporter.json or creating mcporter.jsonc fails with Operation not permitted, and ~/.claude.json is still denied.

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