docs: add pre-push checklist to AGENTS.md

Amp-Thread-ID: https://ampcode.com/threads/T-019c66f5-f25d-701a-9ea4-deb56277f474
Co-authored-by: Amp <amp@ampcode.com>

Author: tsenart

AGENTS.md

@@ -73,11 +73,23 @@ CLI (clap)
 ```sh
 cargo build              # Debug build
 cargo build --release    # Release (LTO=fat, codegen-units=1)
-cargo test --all         # Run all 90 tests
+cargo test --all         # Run all tests
 cargo fmt --check        # Verify formatting
-cargo clippy -- -D warnings  # Lint (CI runs this, must pass)
+cargo clippy -- -D warnings  # Lint — CI treats warnings as errors
 ```
 
+### Pre-push checklist
+
+**Run all three before every push.** CI will reject the PR/push if any fail.
+
+```sh
+cargo fmt
+cargo clippy -- -D warnings
+cargo test --all
+```
+
+This is non-negotiable. Don't push and hope CI passes.
+
 ## CI & Release
 
 CI runs on every push/PR via `.github/workflows/ci.yml`. Three jobs: