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
• preserve/strengthen runtime capability checks where needed

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 plugin.json to the development sentinel, removing the auto-sync workflow, and adding a post-build validation step in the release workflow to ensure the shipped manifest matches the release tag.

Changes:

• Reset plugin.json version to 0.0.0 sentinel
• Delete obsolete sync-plugin-version.yml workflow
• Add post-build validate-contract --for-publish step in release workflow

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
plugin.json	Version reset to 0.0.0 development sentinel
.github/workflows/sync-plugin-version.yml	Removed obsolete tag-triggered sync workflow
.github/workflows/release.yml	Added post-build validation of shipped plugin.json against release tag

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