feat(KLEF-120): Add layer tag constants

[NathanRoos]

Pull Request

Summary

Adds exported Tag constants to the SDK so plugin authors writing Go plugins can reference them instead of raw strings.

Related Issues

Closes #

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Changes

What's Included

v1/types.go — added TagFrontend, TagBackend, TagIdentity, TagDevOps constants

What's Not Included

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Testing

How Was This Tested?

Documentation/constants only — no logic changes.

Test Coverage

• Unit tests added or updated
• Integration tests added or updated
• Manually tested end-to-end

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Breaking Changes

Does this PR introduce breaking changes?

• Yes
• No

If yes, describe the impact and any required migration steps:

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Security Considerations

• This PR affects authentication or authorization logic
• This PR touches secrets, tokens, or environment variables
• This PR affects infrastructure, deployment pipelines, or network configuration

If any box is checked, describe the security impact and any mitigations applied:

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Documentation

Does this PR require documentation updates?

• Yes
• No

If yes, check all that apply:

• README.md
• ARCHITECTURE.md
• API reference
• Architecture diagrams (C4 / DDD)
• /docs

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UI/UX (If Applicable)

• Includes new components or views
• Changes styles or theme tokens
• Responsive behavior verified
• Requires design approval

Screenshots or recordings:

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Pre-Merge Checklist

• PR title follows semantic format (feat:, fix:, chore:, docs:, refactor:, test:)
• All CI checks passing
• Code follows project style guidelines
• No debug logs or commented-out code left in
• Dependencies reviewed (no unnecessary additions)
• No sensitive information included

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Reviewer Notes