Fix CLI datetime parsing to default date-only strings to midnight instead of current time

[Copilot]

The CLI was incorrectly interpreting date-only strings like --until 2025-08-06 by using the current time instead of defaulting to 00:00:00 (midnight). This caused unexpected behavior where users expected the date to represent the start of the day.

Problem

When using the CLI with date-only parameters, the FuzzyDateTime class was using parsedatetime.Calendar().parseDT() which defaults to the current time for the time component:

# User expects this to mean "2025-08-06 00:00:00"
dispatch-cli create 1 test BATTERY "2025-08-06" 1h --until "2025-08-06"

# But it was interpreted as "2025-08-06 14:30:15" (current time)

Solution

Added intelligent detection of date-only strings using regex patterns to distinguish between:

• Date-only formats: 2025-08-06, 2025/08/06, 08/06/2025, 08-06-2025
• Relative expressions: in 1 hour, tomorrow, in 2 days

For date-only strings, the parser now uses a sourceTime parameter set to midnight, ensuring consistent behavior. Relative time expressions continue to use the current time as the reference point.

Changes

• Modified FuzzyDateTime.convert() in _cli_types.py to detect date-only patterns
• Added regex patterns for common date formats (ISO, slash, US, dash formats)
• Preserved all existing functionality for relative time expressions and explicit datetime strings

Testing

• All existing CLI tests continue to pass
• Date-only strings now correctly default to midnight (00:00:00)
• Relative time expressions like "in 1 hour" still work as expected
• Multiple date formats are supported consistently

Fixes #198.

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