Replace Manual Time Input with Step Buttons in Settings Panel

[AkshayAshokCode]

Replace the manual input fields for Session Duration and Break Duration in PomodoroSettingsPanel with step-based + and – controls. Each click should increment/decrement the value by 5 minutes, within predefined min/max bounds.

Scope:

Apply to session and break durations
Minimum/maximum limits:
Session: 5–120 min
Break: 1–60 min
Disable +/– buttons at limits
Retain validation and apply logic for "Sessions per Round" as is
Retain error message popup if needed