Refactor: Standardize and Improve Logging Consistency

[fred-maina]

Description

Logging is inconsistent across the application. Some log messages are unhelpful, and log levels are not always used appropriately.

Examples:

1. Unhelpful message: In AuthController.checkUsername, the log log.error("username {} not found for some weird reason", username); is not professional or helpful for debugging. It should be a log.warn or log.info stating the username was checked and not found.
2. Inconsistent Levels: Some debug-level information is logged at INFO (e.g., in ChatWebSocketHandler).
3. Missing Logs: Critical paths, like the default case in ChatWebSocketHandler.handleTextMessage, log a warning but could be more verbose about the payload received.

Acceptance Criteria

1. Audit all log statements in the project.
2. Standardize log levels:
   • ERROR: For unrecoverable errors (e.g., database connection failure, unhandled exceptions in ControllerAdvice).
   • WARN: For recoverable issues or potential problems (e.g., invalid auth token, user not found, unhandled WebSocket message type).
   • INFO: For major lifecycle events (e.g., application started, user logged in, new user registered, session connected/disconnected).
   • DEBUG: For granular, high-volume information (e.g., "message received", "checking cache", "sending token request").
3. Rewrite unhelpful messages: Change messages like "...for some weird reason" to be professional and state the facts.
4. Ensure all exceptions are logged with the stack trace at the ERROR or WARN level.