ci: add Docker multi-distro tests, renovate, rust-toolchain

- Add Docker test matrix (debian/alpine/fedora) to GitHub Actions CI
- Add renovate.json for automated dependency updates
- Add rust-toolchain.toml for contributor convenience

.github/workflows/ci.yml

@@ -58,3 +58,13 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
       - uses: EmbarkStudios/cargo-deny-action@v2
+
+  test-docker:
+    name: Test (${{ matrix.target }})
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target: [debian, alpine, fedora]
+    steps:
+      - uses: actions/checkout@v4
+      - run: docker compose run --rm ${{ matrix.target }} cargo test --workspace

renovate.json

@@ -0,0 +1,5 @@
+{
+  "extends": [
+    "config:recommended"
+  ]
+}

rust-toolchain.toml

@@ -0,0 +1,3 @@
+[toolchain]
+channel = "stable"
+components = ["rustfmt", "clippy"]