contributing: link to rename-safety contract

The agent at nativeapptemplate-agent mechanically renames Shop, Shopkeeper,
and ItemTag across all case forms when generating customized projects.
Some substrate patterns ("Swipe an item tag to ...") read correctly here
but produce ungrammatical output ("Swipe an patient to ...") after the
rename pipeline substitutes a consonant-starting word.

The canonical conventions for substrate maintainers live in
docs/SUBSTRATE-CONTRACT.md in the agent repo. Linking from CONTRIBUTING
so future PRs touching user-facing strings see the rules before merging.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dadachi

CONTRIBUTING.md

@@ -48,6 +48,16 @@ Architecture: Simple MVVM Layered Architecture with `@Observable` state manageme
 - Tests use [Swift Testing](https://developer.apple.com/xcode/swift-testing/).
 - Place new tests alongside existing ones mirroring the source structure.
 
+## Rename safety
+
+This substrate is consumed by [`nativeapptemplate-agent`](https://github.com/nativeapptemplate/nativeapptemplate-agent), which mechanically renames `Shop`, `Shopkeeper`, and `ItemTag` (and all their case forms — PascalCase, snake_case, camelCase, flat, UPPER_SNAKE, humanized lower/title/sentence × singular/plural) to user-chosen target words. Some patterns that read fine in this repo break when renamed.
+
+Before merging changes that touch user-facing strings, test descriptors, or comments mentioning domain entities, read the [substrate rename-safety contract](https://github.com/nativeapptemplate/nativeapptemplate-agent/blob/main/docs/SUBSTRATE-CONTRACT.md).
+
+**Quick rule of thumb:** avoid `"a"` / `"an"` directly preceding `Shop`, `Shopkeeper`, or `ItemTag` (or their humanized forms) — write self-contained or article-free phrasings instead.
+
+**Failure mode this prevents:** a string like `"Swipe an item tag to ..."` reads correctly here but produces `"Swipe an patient to ..."` after the rename pipeline substitutes a consonant-starting word like `Patient`.
+
 ## Development Setup
 
 See [README.md](README.md) for full setup instructions.