Add Dalamud API13 compatibility

[kirin-xiv]

Summary

This PR adds API13 compatibility to BDTH. I had originally updated my fork for personal use when the API transition happened, and am now contributing the changes back upstream for the community.

Changes Made

• Project file: Added <DalamudApiLevel>13</DalamudApiLevel> property
• SDK: Already using Dalamud.NET.Sdk/13.0.0

Testing

• Builds successfully with 2 existing warnings (unrelated to API13)
• Plugin loads and functions correctly in-game
• Note: Plugin validation shows "no config UI callback" warning, but functionality is intact

Context

I needed BDTH working with API13 for my own setup, so I made these minimal changes in my fork. Since the plugin works well with these updates, I thought it would be helpful to contribute them back so other users can benefit from continued API13 compatibility.

This is a minimal change that brings BDTH up to date with the latest Dalamud API requirements without disrupting existing functionality.

[jackandcarter]

I'm also working on finishing the work on the other branch to help out, its done just have to test, and your contribution will also help make that happen, so thanks :P

[LeonBlade]

Are we sure this is necessary?

[kirin-xiv]

It's not necessary. Tested after removing it and its fine.

[kirin-xiv]

TIL I don't have to explicitly define the API level in my plugins lol