feat: add credits modal and update docker config

- Add credits modal showing project creators and libraries used
- Replace bottom-of-canvas credits with clickable credits button
- Update docker-compose to pull pre-built image from git.azuze.fr registry
- Simplify README Docker instructions

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -1,12 +1,6 @@
 services:
   motionity:
-    build:
-      context: .
-      # WITH_FFMPEG: "0" trims 18.5 MB by fetching the MP4/GIF encoder from
-      # archive.org at runtime instead of shipping it.
-      args:
-        WITH_FFMPEG: "1"
-    image: motionity:latest
+    image: git.azuze.fr/kawa/motionity:latest
     ports:
       - "8080:8080"
     restart: unless-stopped