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 the "plugin version discipline" pattern: the committed plugin.json keeps the 0.0.0 development sentinel, and the release workflow gains a post-build check that the shipped manifest matches the pushed tag.

Changes:

• Reset plugin.json version to the 0.0.0 development sentinel.
• Add a post-build validate-contract --for-publish --tag ... --release-dir . step in release.yml to verify the shipped manifest carries the release tag.

Reviewed changes

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

File	Description
plugin.json	Set version to the 0.0.0 sentinel so the committed manifest no longer encodes a release version.
.github/workflows/release.yml	Add post-build validate-contract step that asserts the shipped manifest matches github.ref_name.

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