Scaffold the emote library with a Stonecutter Fabric mod and tester

- core/: Minecraft-independent animation model (Bone, BoneTransform with
  bend fields, Pose, Animation, AnimationPlayer) with JUnit tests.
- src/main: Fabric mod built for 1.21.4-1.21.11 with Stonecutter on
  Mojang mappings. Samples each player's pose into its render state and
  applies it at the end of HumanoidModel.setupAnim (armor follows too).
- src/testmod: dev-only tester with /emotes play|stop|info and a mixin
  audit on startup.
- Publishing to the saturnclientmc Gitea Maven registry as
  org.saturnclient:emotes-core and emotes-fabric:<v>+<mc>.

Loom is pinned to 1.17 because 1.18 needs a Java 25 JVM.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/testmod/resources/fabric.mod.json

@@ -0,0 +1,16 @@
+{
+  "schemaVersion": 1,
+  "id": "saturn_emotes_testmod",
+  "version": "${version}",
+  "name": "Saturn Emotes Tester",
+  "description": "Dev-only commands for trying Saturn Emotes in game.",
+  "license": "Apache-2.0",
+  "environment": "client",
+  "entrypoints": {
+    "client": ["org.saturnclient.emotes.testmod.EmotesTestmod"]
+  },
+  "depends": {
+    "saturn_emotes": "*",
+    "fabric-command-api-v2": "*"
+  }
+}