[general-purpose] Test stacked PR workflow

[sylvansys]

Parent Issue: #321
Agent Type: general-purpose
Branch: 321-feature/can-u-integrate-changes-from-httpsgithub

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Task Description

Test stacked PR workflow

Task Prompt

Create a test file to verify the stacked PR workflow:

1. Create file plugins/github-orchestration/test-stacked-pr.md with content:

# Stacked PR Test

Created at: [timestamp]
Purpose: Test that SubagentStop hook creates PR correctly

This file tests:
- Branch creation on SubagentStart
- Commit and push on SubagentStop
- PR creation with proper title/body

2. Fill in the actual timestamp.

This tests the full stacked PR workflow including the PR creation fix.