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

This PR enforces “plugin version discipline” by keeping the repo’s committed plugin.json at a development sentinel version while shifting release-time correctness checks into the release workflow (and removing the prior tag-triggered sync workflow).

Changes:

• Set committed plugin.json.version to 0.0.0 (development sentinel).
• Remove the obsolete sync-plugin-version GitHub Actions workflow.
• Add a post-build wfctl plugin validate-contract step intended to validate the shipped manifest against the release tag.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
plugin.json	Sets the committed manifest version to the 0.0.0 development sentinel.
.github/workflows/sync-plugin-version.yml	Removes the tag-driven workflow that previously opened PRs to sync plugin.json version.
.github/workflows/release.yml	Adds post-build validation intended to ensure the released manifest matches the tag.

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