Nitwit 1.2.1 Stability Patch

Purpose
- Makes adaptive behavior less disruptive by default.
- Automatically adapts particle quality only.
- Leaves render distance, entity visibility distance, and simulation distance unchanged by default.
- Uses slower overload escalation/recovery settings.
- Migrates a complete untouched Nitwit 1.2.0 default config to the safer defaults; customized configurations are preserved.
- Updates the declared Minecraft range to >=26.0 <26.4 and mixin compatibility metadata to JAVA_25.

Important limitations
This is a stability/configuration patch, not a completed all-in-one optimization engine. It does not implement renderer/entity/chunk-generation algorithms comparable to Sodium, Lithium, C2ME, or other specialized mods. It cannot force lower network ping or fix remote-server TPS/authoritative action delays from the client. Game launches on each listed version and mixed-mod combinations have not been run in this environment.

Testing
The replacement configuration class compiled with Java 21, config-default smoke tests passed, legacy default-config migration passed, and the JAR/metadata were validated offline. Native Fabric Loom builds, launch tests, and in-game benchmarks remain outstanding.
