ci: add publish workflow, binary attestation, and dev extras

- publish.yml: automated PyPI/npm/Docker on v* tag push; OIDC trusted publishing for PyPI/npm; Docker signed with Cosign keyless + provenance attested
- attest-release.yml: manual workflow to attest binary release assets via Sigstore (actions/attest-build-provenance@v2)
- pyproject.toml: add dev extras (pytest, pytest-asyncio)

.github/workflows/attest-release.yml

@@ -0,0 +1,28 @@
+name: Attest Release Binary
+
+on:
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Release tag (e.g. chromium-v145.0.7632.159.2)'
+        required: true
+
+jobs:
+  attest:
+    runs-on: ubuntu-latest
+    permissions:
+      id-token: write      # Sigstore OIDC
+      attestations: write  # GitHub attestation API
+      contents: write      # Download release assets
+    steps:
+      - name: Download release binaries
+        run: gh release download ${{ github.event.inputs.tag }} --repo CloakHQ/cloakbrowser --pattern "cloakbrowser-*.tar.gz" --pattern "cloakbrowser-*.zip"
+        env:
+          GH_TOKEN: ${{ github.token }}
+
+      - name: Attest build provenance
+        uses: actions/attest-build-provenance@v2
+        with:
+          subject-path: |
+            cloakbrowser-*.tar.gz
+            cloakbrowser-*.zip