ci: add build/test/clippy gate + cargo audit; pin rust-version

Oracle P2 plan step 1+2+missed-fields. Locks in the audit cleanup so
future PRs can't regress the 0-errors / deny-unsafe / 79-tests baseline.

  - .github/workflows/ci.yml: two jobs on ubuntu-latest (Linux only —
    project is Wayland/VAAPI-specific, no macOS/Windows story).
      * build-test: installs ffmpeg + libavcodec/libavformat/libavutil/
        libswscale/libva dev + libwayland + libdrm + libpipewire-0.3-dev
        + libclang-dev/llvm-14 (LIBCLANG_PATH pinned); caches cargo +
        target; runs clippy -> build --release -> test --release.
        Release build before tests is mandatory because
        tests/integration_test.rs shells out to target/release/wl-webrtc.
      * audit: installs cargo-audit and runs 'cargo audit --deny warnings'
        as a separate job so a RUSTSEC advisory fails the build
        independently of compile state.
    No -D warnings on clippy yet — undocumented_unsafe_blocks is already
    deny via Cargo.toml; remaining warnings are advisory and can be
    tightened later.

  - Cargo.toml: pin rust-version = '1.70' to match README's claim.
    Without this, cargo builds silently on older toolchains and surfaces
    errors as cryptic parse failures instead of a clean version-mismatch
    message. Oracle flagged this as a missing field during P2 review.

License field intentionally omitted — repo has no LICENSE file and no
publication plan yet. Add when publication becomes a goal.

Verified locally: YAML parses, cargo build --release Finished in 9.82s,
cargo test --release 79 passed, cargo clippy 0 errors.

.github/workflows/ci.yml

@@ -0,0 +1,89 @@
+# Continuous integration for wl-webrtc.
+#
+# Triggered on push/PR to master. Runs the full quality gate that the recent
+# audit baselined:
+#   - clippy: 0 errors (undocumented_unsafe_blocks is deny in Cargo.toml; other
+#     warnings are advisory for now).
+#   - build --release: integration tests in tests/integration_test.rs shell out
+#     to target/release/wl-webrtc, so the release binary must exist before tests
+#     run.
+#   - test --release: 79 unit + 3 integration; the 1 hardware-ignored test
+#     stays ignored in CI (needs Wayland session + VAAPI GPU).
+#   - cargo audit: separate job so a RUSTSEC advisory fails the build without
+#     conflating with compile errors.
+#
+# The job pins Linux only — the project is Wayland/VAAPI-specific and has no
+# macOS/Windows story. Oracle audit 2026-06-28 P2 plan.
+
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+env:
+  CARGO_TERM_COLOR: always
+  # Build dependencies match shell.nix + README Prerequisites section.
+  LIBCLANG_PATH: /usr/lib/llvm-14/lib
+
+jobs:
+  build-test:
+    name: Build + Clippy + Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain (stable)
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            ffmpeg \
+            libavcodec-dev libavformat-dev libavutil-dev libswscale-dev libva-dev \
+            libwayland-dev wayland-protocols \
+            libdrm-dev \
+            libpipewire-0.3-dev \
+            libclang-dev llvm-14
+
+      - name: Cache cargo registry + build artifacts
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('Cargo.lock', 'Cargo.toml') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Clippy (release, all targets)
+        run: cargo clippy --release --all-targets
+
+      - name: Build release (required before tests)
+        run: cargo build --release --all-targets
+
+      - name: Test (release)
+        run: cargo test --release
+
+  audit:
+    name: Security audit (RUSTSEC)
+    runs-on: ubuntu-latest
+    # Keep separate from build-test so a vulnerability advisory fails the
+    # check independently of compile state.
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain (stable)
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Install cargo-audit
+        run: cargo install cargo-audit --locked
+
+      - name: Audit dependencies
+        run: cargo audit --deny warnings