Mobhighlight

Compatibility fix for Fabric Loader 0.18.x.

**What was wrong**

- 2.3.0 required Fabric Loader 0.19 or newer, but the mod only uses loader APIs that have been around for years.
- The floor was taken from the development environment instead of from what the mod actually needs.
- On instances running Fabric Loader 0.18.x - common in larger modpacks - the game refused to launch with `HARD_DEP_NO_CANDIDATE`, listing Mob Highlight as the blocking mod.

**What changed**

- Minimum Fabric Loader lowered from 0.19 to 0.18.4.
- That is the only change. No new features, no config changes, no behaviour changes, and existing settings carry over untouched.

**Who should update**

- Required if you run Fabric Loader 0.18.x - 2.3.0 cannot load there at all.
- Optional on 0.19 or newer. Worth doing anyway so everyone stays on the same build.

**Requirements**

- Minecraft 1.21.11
- Fabric Loader 0.18.4 or newer
- Fabric API
- Java 21
- Client-side only