feat: Validate GAT ver claim supported version

[clement0010]

Changes

• Validate that the GAT ver claim equals "1" in GATClaims.Validate(), returning jwt.ErrTokenInvalidClaims for unsupported versions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.40%. Comparing base (81b7a3d) to head (62a4f71).
⚠️ Report is 4 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #228      +/-   ##
==========================================
+ Coverage   82.39%   82.40%   +0.01%     
==========================================
  Files          35       35              
  Lines        2590     2592       +2     
==========================================
+ Hits         2134     2136       +2     
  Misses        346      346              
  Partials      110      110              

Flag	Coverage Δ
integration	48.24% <0.00%> (+0.04%)	⬆️
unit	77.19% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
internal/token/gat_claims.go	100.00% <100.00%> (ø)

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[Copilot]

Pull request overview

This PR enforces a single supported version for GAT tokens by validating that the ver claim equals "1" during GATClaims.Validate(), and ensures unsupported versions surface as jwt.ErrTokenInvalidClaims.

Changes:

• Add a supportedVersion constant and reject any ver claim not equal to "1" in GATClaims.Validate().
• Introduce a dedicated errUnsupportedVersion sentinel error and wrap it under jwt.ErrTokenInvalidClaims.
• Add a unit test covering the unsupported-version validation path.

Reviewed changes

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

File	Description
internal/token/gat_claims.go	Adds explicit ver-value validation against a supported version and returns jwt.ErrTokenInvalidClaims for unsupported versions.
internal/token/gat_claims_test.go	Adds a test case asserting unsupported ver values are rejected with the expected JWT error and message substring.

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[minhtule]

LGTM 👍