Add AGENTS build instructions

AGENTS.md

@@ -0,0 +1,22 @@
+# AGENTS
+
+## Requirements
+- macOS 13.0+ (Ventura)
+- Xcode 15+
+- Access to a self-hosted Memos instance for runtime testing
+
+## Build
+- Open `FastMemos.xcodeproj` in Xcode and build with `⌘B`
+- CLI build:
+```bash
+xcodebuild -project FastMemos.xcodeproj -scheme FastMemos -configuration Debug build
+```
+
+## Run
+```bash
+xcodebuild -project FastMemos.xcodeproj -scheme FastMemos -configuration Debug build
+open ./build/Debug/FastMemos.app
+```
+
+## TODO
+- Document any additional workflows or scripts not covered in README/CLAUDE.