login: smoother create splitting (fixes #13083)

[dogi]

🎯 What: The code health issue addressed
Refactored the monolithic onCreate method in LoginActivity by extracting blocks of initialization logic into descriptive helper methods.

💡 Why: How this improves maintainability
The original onCreate method was over 110 lines long, making it difficult to read and understand the initialization flow. By breaking it down into focused methods, the overall logic becomes declarative, easier to test, and simpler to maintain.

✅ Verification: How you confirmed the change is safe
Ran compileDefaultDebugKotlin to ensure syntax correctness, and executed testDefaultDebugUnitTest to confirm no existing functionality was broken. The refactoring maintained the original execution sequence closely, minimizing risks. Code review was also performed and approved the changes.

✨ Result: The improvement achieved
onCreate is now a clean, ~25-line method that clearly outlines the initialization steps of LoginActivity.

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PR created automatically by Jules for task 2880981485448130640 started by @dogi

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