Improve cross-repo task modeling

[justguy]

Tracker task: t20
Tracker: llm-tracker
Swimlane: improvements
Priority: p2

Goal

Make cross-repo work first-class by modeling primary repo, secondary repo, per-repo allowed paths, and approval requirements for cross-repo edits.

Current note

Cross-repo work is representable today, but not first-class enough for reliable execution and approval flows.

Tracker context

• Created from the live llm-tracker improvements swimlane backlog.
• Keep the tracker row and the GitHub issue aligned as this work evolves.