docs: agent instructions and a before/after PR template

.github/pull_request_template.md

@@ -0,0 +1,17 @@
+<!-- Screenshots: `gh pr create --body-file <body> --attach screenshots/before.png --attach screenshots/after.png`
+uploads both and rewrites the links below. In the browser, drag each image into its cell instead. -->
+
+<!-- One line: what changed and why. -->
+
+| Before | After |
+| --- | --- |
+| ![Before](./screenshots/before.png) | ![After](./screenshots/after.png) |
+
+### How it was verified
+
+- **Device:** <!-- simulator name, model and runtime, e.g. stim-tour (iPhone 18 Pro, iOS 27.0) -->
+- **Readiness:** <!-- e.g. Stim waited for the app to report ready (3.5s) -->
+- **Build:** <!-- build time, and whether it came from Stim's cache -->
+- **Logs:** <!-- result of stim logs --errors -->
+
+Built and verified with [Stim](https://github.com/appandflow/stim).

.gitignore

@@ -5,3 +5,4 @@ dist/
 /android
 *.log
 .DS_Store
+/screenshots/

AGENTS.md

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+# Agent instructions
+
+This is the Stim tutorial app. Follow `stim guide tutorial run` (or `npx stim guide tutorial run` when `stim` is not installed).
+
+Before you open a pull request, follow `stim guide tutorial share`.

CLAUDE.md

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+@AGENTS.md

README.md

@@ -17,7 +17,7 @@ If `stim` is installed globally, drop `npx`. The Android version is `stim androi
 
 ## Tutorial pull requests
 
-The last tutorial step can open a pull request to this repo with a screenshot at `finish/<github-login>.png`. A workflow (`.github/workflows/tutorial-finish.yml`) comments, adds the `tutorial-finish` label and closes the PR without merging. It uses `pull_request_target` and only calls the GitHub API; it never checks out or runs the PR's code.
+The optional share step can open a pull request to this repo with before and after screenshots of your change, following `.github/pull_request_template.md` (older Stim versions commit one screenshot at `finish/<github-login>.png`). A workflow (`.github/workflows/tutorial-finish.yml`) comments, adds the `tutorial-finish` label and closes the PR without merging. It uses `pull_request_target` and only calls the GitHub API; it never checks out or runs the PR's code.
 
 ## License