fix: accept boolean values for permission config

[itstrivial]

Fixes #7810

What does this PR do?

Users may now use boolean true/false instead of "allow"/"deny" for permissions. This adds a preprocess step to convert booleans automatically, consistent with how tools config already handles this.

How did you verify your code works?

I created .opencode/agent/testing.md with the following permissions:

---
description: Test agent
mode: subagent
tools:
  read: true
permission:
  write: false
---

I then launched OpenCode in my project directory. It now launches successfully and does not hang like before.