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 plugin version discipline by resetting the committed plugin.json version to the development sentinel and adding a post-build validation step in the release workflow to ensure the shipped manifest carries the release tag.

Changes:

• Reset plugin.json version from 1.0.2 back to the 0.0.0 development sentinel.
• Add a post-build wfctl plugin validate-contract --for-publish step in release.yml that checks the shipped manifest against github.ref_name and the release dir.

Reviewed changes

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

File	Description
plugin.json	Reverts version field to the 0.0.0 sentinel so the source of truth for releases is the git tag.
.github/workflows/release.yml	Adds a post-build validate-contract step verifying the shipped plugin.json against the pushed tag.

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