ShyamDuels

feat: add configurable duel titles and fix kit editor issues

This commit introduces a fully configurable duel title system and fixes critical kit editor bugs affecting gameplay stability.

──────────────────────── Duel Title System ────────────────────────

• All duel titles and subtitles are now configurable via messages.yml
• Supports countdown, fight, win, loss, round-win, and round-loss titles
• Dynamic placeholder support:
  • {round}, {max_rounds}, {score}
  • Countdown-only: {seconds}, {color}
• Automatic countdown color system:
  • Green (5–4), Yellow (3–2), Red (1)
• Supports legacy color codes (&) and MiniMessage formatting
• Subtitles can be disabled individually
• Reload support via /shyamduels reload
• No code changes required for customization

──────────────────────── Kit Editor Fixes ────────────────────────

• Fixed offhand items not saving/loading correctly
• Replaced display-name checks with PDC-based placeholder detection
• Prevents placeholder shields from being saved as real items
• Real shields and items now work correctly in offhand
• Added strict armor slot validation to prevent misplacement
• Validates armor types on both click and drag events
• Supports all vanilla armor, elytra, turtle helmet, pumpkins, and mob heads
• Sends configurable feedback message on invalid armor placement

──────────────────────── Technical Notes ────────────────────────

• Added ItemBuilder PDC tag support
• O(1) validation logic with negligible performance impact
• Fully backward compatible with existing kits
• No database or configuration migrations required

This update significantly improves visual customization and ensures reliable, predictable kit behavior in-game.