chore: apply plugin version discipline

[intel352]

Part of GoCodeAlone/workflow#760.

Changes:

• keep committed plugin.json.version at the 0.0.0 development sentinel
• 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 in-tree plugin.json to the 0.0.0 development sentinel (GoReleaser injects the real tag at release time) and adds a post-build verification step that re-runs wfctl plugin validate-contract --for-publish against the release artifacts to confirm the shipped manifest carries the tag.

Changes:

• Reset plugin.json version to 0.0.0 sentinel.
• Add post-build validate-contract step using --release-dir . in release.yml.

Reviewed changes

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

File	Description
plugin.json	Version reset to 0.0.0 dev sentinel; tag is injected at release.
.github/workflows/release.yml	New post-build step validates that shipped plugin.json carries the release tag.

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