167-Feature add /convert-time command

[RemainingDelta]

Changes

• Added /convert-time slash command that converts a date and time into all 7 Discord timestamp formats with copyable raw strings
  • date — Date in YYYY-MM-DD format (e.g. 2026-03-27)
  • time — Time in H:MM AM/PM format (e.g. 8:13 PM)
  • timezone — Abbreviation (e.g. EST, PT) or IANA name (e.g. America/New_York)
• Supports common timezone abbreviations mapped to their proper IANA timezones to handle DST correctly

Screenshots

Command being used:

Closes #167