Clean repo for open source release

Remove build artifacts, dev tool configs, unused dependencies,
and third-party source dumps. Add proper README, update .gitignore,
clean up Makefile.

src/main/java/com/tiedup/remake/mixin/MixinLivingEntityBodyRot.java

@@ -0,0 +1,56 @@
+package com.tiedup.remake.mixin;
+
+import com.tiedup.remake.state.HumanChairHelper;
+import com.tiedup.remake.v2.BodyRegionV2;
+import com.tiedup.remake.state.PlayerBindState;
+import net.minecraft.world.entity.LivingEntity;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.item.ItemStack;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+/**
+ * Mixin to lock player body rotation during human chair mode.
+ *
+ * Vanilla {@code LivingEntity.tickHeadTurn()} gradually rotates yBodyRot
+ * toward the head/movement direction. This overrides any value set from
+ * a tick handler. By cancelling the method here, the body stays locked
+ * at the stored facing direction.
+ */
+@Mixin(LivingEntity.class)
+public abstract class MixinLivingEntityBodyRot {
+
+    @Inject(method = "tickHeadTurn", at = @At("HEAD"), cancellable = true)
+    private void tiedup$lockBodyForHumanChair(
+        float yRot,
+        float animStep,
+        CallbackInfoReturnable<Float> cir
+    ) {
+        LivingEntity self = (LivingEntity) (Object) this;
+        if (!(self instanceof Player player)) {
+            return;
+        }
+
+        PlayerBindState state = PlayerBindState.getInstance(player);
+        if (state == null || !state.isTiedUp()) {
+            return;
+        }
+
+        ItemStack bind = state.getEquipment(BodyRegionV2.ARMS);
+        if (bind.isEmpty()) {
+            return;
+        }
+
+        if (!HumanChairHelper.isActive(bind)) {
+            return;
+        }
+
+        // Lock body rotation to the stored facing and skip vanilla update
+        float lockedYaw = HumanChairHelper.getFacing(bind);
+        self.yBodyRot = lockedYaw;
+        self.yBodyRotO = lockedYaw;
+        cir.setReturnValue(animStep);
+    }
+}