ci: run tests, fuzz smoke and docs checks on GitHub Actions

Offline test suite on Ubuntu and Windows, a random-input fuzz smoke per
parser target, and docs/check-docs.sh on every push to main and PR.

.github/workflows/ci.yml

@@ -0,0 +1,87 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+# Cancel superseded runs of the same branch/PR.
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+env:
+  DOTNET_NOLOGO: true
+  DOTNET_CLI_TELEMETRY_OPTOUT: true
+
+jobs:
+  test:
+    name: Test (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 20
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 10.0.x
+
+      # Build/test only the test project and what it references (Core, Fuzz, ServerProbe):
+      # the Android head needs a workload and SDK that CI does not provision.
+      - name: Restore
+        run: dotnet restore tests/PalladiumWallet.Tests
+
+      - name: Build
+        run: dotnet build tests/PalladiumWallet.Tests --no-restore -c Release
+
+      # Offline and deterministic: unit, property-based (CsCheck), fuzz-corpus replay and the
+      # in-process FakeElectrumServer tests. LiveServerTests is a no-op without
+      # PALLADIUM_TEST_SERVERS, so no third-party server is contacted.
+      - name: Test
+        run: >
+          dotnet test tests/PalladiumWallet.Tests --no-build -c Release
+          --logger "trx;LogFileName=test-results.trx"
+          --collect:"XPlat Code Coverage"
+          --results-directory TestResults
+
+      - name: Upload test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-results-${{ matrix.os }}
+          path: TestResults
+          retention-days: 14
+
+  fuzz-smoke:
+    name: Fuzz smoke (${{ matrix.target }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    strategy:
+      fail-fast: false
+      matrix:
+        target: [header, merkle, slip132, bip39, address, coinamount, walletdoc, encfile, peers]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 10.0.x
+      # Random-input smoke run of each untrusted-input parser; any escaping exception fails the job.
+      # The coverage-guided campaign (afl++) stays a manual step, see tests/PalladiumWallet.Fuzz/fuzz.sh.
+      - name: Fuzz ${{ matrix.target }}
+        run: dotnet run -c Release --project tests/PalladiumWallet.Fuzz -- ${{ matrix.target }} --random 20000
+
+  docs:
+    name: Docs checks
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+      - name: Check docs
+        run: ./docs/check-docs.sh