fix(release): serialize canonical draft creation

[syzsunshine219]

Summary

• Automatically create Draft Releases only for merged MemTensor:release/vX.Y.Z → main pull requests.
• Keep workflow_dispatch as the explicit smoke/recovery entry point.
• Serialize automatic and manual Draft Release mutations through one job-level concurrency group with queue: max and no cancellation.
• Tighten the release-branch parser to require the exact release/vX.Y.Z form.

Incident prevented

Merging both v1.0.8 → main and release/v1.0.8 → main emitted two merged-PR events. Their different concurrency groups allowed both jobs to create and mutate the same Draft Release concurrently, so asset upload and cleanup interfered with each other. Bare v* and fork release PRs now skip the release job; canonical and manual runs queue instead of racing.

Verification

• Regression assertions failed against the previous dual-trigger/raw-group workflow.
• npm run test:release-workflow: 20/20 passed.
• Project Harness Full Gate passed on 553b5d342df0cda6dc4877836a794f6162e1edf6.
• Independent diff review found no P0/P1 issues; the requested exact boolean-grouping regression assertion is included.

[syzsunshine219]

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