Add 24-hour clock option for flight time inputs

[EricGrill]

Summary

• Adds a new use24HourFormat setting to allow users to toggle between 12-hour (with AM/PM) and 24-hour time formats
• Creates a new TimeInput component that conditionally renders either a native time input (24-hour mode) or a time input with AM/PM selector (12-hour mode)
• Integrates the new TimeInput component into the New Flight and Edit Flight forms
• Adds a toggle in Settings under the Customization section

Closes #15

Test plan

• Verify the "Use 24-hour time format" checkbox appears in Settings > Customization
• With 24-hour format disabled (default), verify time inputs show AM/PM selector
• With 24-hour format enabled, verify time inputs use native 24-hour format
• Create a new flight with times in both modes and verify they are saved correctly
• Edit an existing flight's times in both modes and verify changes are saved correctly
• Verify the setting persists across page reloads (stored in localStorage)

🤖 Generated with Claude Code