Port a GitHub App to an Origin App

Run this inside the app's codebase. The output is a porting brief for the team plus a Feedback for Cursor section they can send as is (references/brief.md). This skill plans. It does not write or change code unless the user asks for that after reading the brief. Follow the origin-api skill for the docs and the rules to check first. Two more rules:

1. Find it in the code, do not ask. Read what the app uses out of its source. Anything you cannot find becomes a question for the team.
2. Feedback describes use cases, not the team's code. The team's parts of the brief may cite file:line. Feedback for Cursor says only what the app needs to do and what Origin lacks for it, in Origin terms, with no file paths, module names, framework details, or repository names.

What to find

Record file:line for each item, and note what you looked for but did not find.