chore: add GitHub CI workflow and update format instructions

Add a basic Rust CI pipeline (check, nextest, clippy, format-check)
and update AGENTS.md to use `cargo make format` instead of `cargo fmt`.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Frando

.github/workflows/ci.yml

@@ -0,0 +1,37 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy, rustfmt
+
+      - uses: taiki-e/install-action@cargo-make
+      - uses: taiki-e/install-action@nextest
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Check
+        run: cargo check --workspace --tests
+
+      - name: Test
+        run: cargo nextest run --workspace
+
+      - name: Clippy
+        run: cargo clippy --workspace --tests -- -D warnings
+
+      - name: Format
+        run: cargo make format-check

AGENTS.md

@@ -87,7 +87,7 @@ Run these in order. All must pass with zero warnings and zero errors:
 Always add a timeout to test runs (e.g. 90s).
 
 ```bash
-cargo fmt
+cargo make format                         # NOT cargo fmt; uses project-specific unstable rustfmt options
 cargo clippy -p patchbay --tests --fix --allow-dirty
 cargo check -p patchbay --tests
 cargo nextest run -p patchbay             # use nextest, not cargo test; parallelism in .config/nextest.toml