🧪 Add tests for Me handler using Echo context

[google-labs-jules]

• 🎯 What: The Me handler in the auth module lacked functional tests; only documentation tests were present.
• 📊 Coverage: Added tests to cover successful user profile retrieval, missing/invalid context claims, invalid user ID type, and deleted user.
• ✨ Result: Improved test coverage by adding TestMeAuthentication, TestMeUserNotFound, and TestMeResponseStructure in handler_test.go and refactoring Service to accept db.Querier instead of a concrete *db.Queries to allow dependency injection during tests.

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PR created automatically by Jules for task 10765680297131660183 started by @Gautam7352

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