ci: standardize CI workflows and git hooks

Add ci.yml (compile/fmt/lint/test/audit/machete), nightly.yml (geiger
unsafe audit), deny.toml (license/ban/source policy), and Justfile with
pre-commit, prepush, ci, and install-hooks recipes.

.github/workflows/ci.yml

@@ -0,0 +1,67 @@
+name: CI
+
+on:
+  push:
+    branches: [main, "feature/*", "hotfix/*", "chore/*"]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  compile-check:
+    name: Compile, Format & Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+      - uses: Swatinem/rust-cache@v2
+      - run: cargo check --workspace
+      - run: cargo fmt --all --check
+      - run: cargo clippy --workspace -- -D warnings
+
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    needs: compile-check
+    timeout-minutes: 20
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-nextest
+      - run: cargo nextest run --workspace
+
+  audit:
+    name: Audit & Deny
+    runs-on: ubuntu-latest
+    needs: compile-check
+    if: github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/feature/') || startsWith(github.ref, 'refs/heads/hotfix/')
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - uses: EmbarkStudios/cargo-deny-action@v2
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-audit
+      - run: cargo audit
+
+  machete:
+    name: Unused Dependencies
+    runs-on: ubuntu-latest
+    needs: compile-check
+    if: github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/feature/') || startsWith(github.ref, 'refs/heads/hotfix/')
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-machete
+      - run: cargo machete