fix: implement connection timeout limits and launch splash cut-off

[Michael-128]

Description

Implements network request timeout limits and prevents the app launch splash screen from hanging indefinitely when the active server is offline or slow.

Key Changes

• Global Request Timeout: Configures the default URLSession inside NetworkClient to use a 15-second request and resource timeout interval (down from the default 60 seconds).
• App Launch Splash Cut-off: Races the startup connection task against a 3-second timer using withThrowingTaskGroup. If connection fails to establish within 3 seconds, the login
  task is cancelled and the app falls back to the Server List rather than freezing on the logo screen.
• Telemetry Session Recovery: Catches 401 Unauthorized responses in the background telemetry loop to trigger a silent background re-authentication attempt.
• Unit Tests: Adds testSendRequest_Timeout and testTaskGroup_TimeoutRace to NetworkClientTests to verify request cancellation and timeout propagation.