feat(tui): add 24-hour time format option for session view

[Octane0411]

Description

Adds support for 24-hour time format in the TUI session view, addressing Issue #7208.

Users can now configure whether timestamps in the session view display in 12-hour (AM/PM) or 24-hour format.

Before & After

Before (12-hour format - default)

After (24-hour format)

Changes

• Added time_format configuration option to TUI settings (supports "12h" and "24h" formats)
• Updated time formatting utilities (Locale.time, Locale.datetime, Locale.todayTimeOrDateTime) to accept format parameter
• Applied time format configuration to:
  • Session list view
  • Fork from timeline dialog
  • Timeline view
• Added unit tests for time formatting functions

Configuration Example

Add the following to your opencode.jsonc or .opencode/opencode.jsonc:

{
  "tui": {
    // Use 24-hour time format (default is 12-hour)
    "time_format": "24h"
  }
}

Or use 12-hour format explicitly:

{
  "tui": {
    "time_format": "12h"
  }
}

Testing

• Session list displays correct time format based on configuration
• Fork dialog shows correct time format
• Timeline view respects time format setting
• Unit tests pass for both 12h and 24h formats

Related Issue

Closes #7208