chore: default authentication path to /* in platform-http-main

[Croway]

Summary

• Default the authentication path to /* when not explicitly configured in BasicAuthenticationConfigurer and JWTAuthenticationConfigurer
• Extract shared path resolution logic into MainAuthenticationConfigurer default method
• Add tests for non-root context path and selective path authentication
• Add upgrade guide entry

Test plan

• Existing auth tests pass (Basic + JWT)
• New test: non-root context path with implicit auth path
• New test: explicit authenticationPath for selective protection

[github-actions]

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[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud