Unify Guardian context section collection

[copyberry]

Unify Guardian context section collection

What changed

• Add typed context sections for root-conversation evidence, trusted user answers, and conversation transcripts to codex-guardian-context.
• Use the shared section registry when building core Guardian prompts and asynchronous Guardian V2 scoring context.
• Preserve source-role labeling while delivering authorization evidence as user-role context, and fail closed when context collection fails.

Testing

• Cover shared section ordering and role preservation for synchronous and asynchronous targets.
• Verify trusted user answers appear exactly once as user-role input in Guardian V2 approval flows.