chore: apply plugin version discipline

[intel352]

Part of GoCodeAlone/workflow#760.

Changes:

• keep committed plugin.json.version at the 0.0.0 development sentinel
• remove the obsolete sync-plugin-version workflow when present
• add post-build release validation so the shipped manifest is checked against the tag

Verification:

• wfctl plugin validate-contract .
• wfctl plugin validate-contract --for-publish --tag v9.9.9 .
• GOWORK=off go test ./...

[Copilot]

Pull request overview

Applies “version discipline” for plugin releases by keeping the repo’s committed plugin.json at a development sentinel version and adding a post-build CI check to ensure the release output matches the tag used for publishing.

Changes:

• Set committed plugin.json.version to the 0.0.0 development sentinel.
• Add a post-build wfctl plugin validate-contract --for-publish --tag ... validation step in the release workflow to verify the shipped manifest aligns with the Git tag.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
plugin.json	Keeps the committed manifest at the 0.0.0 dev sentinel version.
.github/workflows/release.yml	Adds post-build release validation to confirm the manifest used for publishing matches the tag.

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