fix(access-keys): load object policy responses

[GatewayJ]

Pull Request

Description

Fix access key policy loading when the canned-policy endpoint returns a structured JSON object. The frontend now normalizes both object responses and legacy JSON strings, preserves statement identifiers, and no longer adds the UI-only Origin field to policy statements sent to the server.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

pnpm install --frozen-lockfile --registry=https://registry.npmmirror.com
pnpm type-check
pnpm lint
pnpm test:run
pnpm format:check

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes rustfs/rustfs#5017

Screenshots (if applicable)

N/A — no visual changes.

Additional Notes

The change is limited to access key policy response normalization and regression coverage.