feat(release): complete CI-based publishing, matching the proven 0.6.9 flow

Verified against the workflow that shipped 0.6.5 -> 0.6.9: it publishes from CI
with pypa/gh-action-pypi-publish via OIDC Trusted Publishing, not by local twine
upload. (RELEASE_NOTES' mention of "twine upload" describes an earlier
iteration; the shipped file uses the action.) Restored the two pieces that were
still missing.

skip-existing: true. PyPI refuses re-uploading a file that already exists, so
without it a run that uploaded 9 of 15 wheels and then failed could never be
retried - the retry dies on the first duplicate and the release is stuck
half-published with no way forward. This is the difference between a recoverable
and an unrecoverable release failure, and it was in the proven flow.

Artifact attestation, non-gating, exactly as commit 49ba957 established:
`continue-on-error: true` and skipped on private repos, because provenance needs
a public repo or GHAS and its absence must never fail an otherwise-good release.
Adds the `attestations: write` permission it requires.

Author: Guillaume Lessard

.github/workflows/release-build.yml

@@ -195,8 +195,9 @@ jobs:
       name: pypi
       url: https://pypi.org/p/qector-decoder-v3
     permissions:
-      id-token: write
+      id-token: write        # PyPI Trusted Publishing (OIDC) — no stored token
       contents: read
+      attestations: write    # build provenance, non-gating (see 49ba957)
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
@@ -251,8 +252,24 @@ jobs:
           pip install twine
           twine check dist/*.whl
 
-      - name: Publish
+      # Non-gating by design: commit 49ba957 ("artifact attestation must not gate
+      # publishing"). Provenance requires a public repo or GHAS, and on a private
+      # repo the API returns "Feature not available", which must not fail a
+      # release that is otherwise good.
+      - name: Generate artifact attestations
+        if: ${{ github.event.repository.private == false }}
+        continue-on-error: true
+        uses: actions/attest-build-provenance@v2
+        with:
+          subject-path: "dist/*"
+
+      - name: Publish to PyPI
         uses: pypa/gh-action-pypi-publish@release/v1
         with:
           packages-dir: dist/
-          attestations: true
+          # Idempotent upload. PyPI rejects re-uploading a file that already
+          # exists, so without this a run that uploaded 9 of 15 wheels and then
+          # failed could never be retried - the retry would die on the first
+          # duplicate and the release would be stuck half-published. With it,
+          # a re-run completes the remaining wheels.
+          skip-existing: true