Bump version to 3.1.1, add mobile portrait layout documentation

- Update version from 2.0.1 to 3.1.1 in pyproject.toml and server/main.py
- Add V3_17_MOBILE_PORTRAIT_LAYOUT.md documenting all mobile improvements:
  responsive layout, animation sizing fixes, compact header, bottom drawers
- Add V3_17 entry to V3 master plan

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/main.py

@@ -325,7 +325,7 @@ async def _close_all_websockets():
 app = FastAPI(
     title="Golf Card Game",
     debug=config.DEBUG,
-    version="2.0.1",
+    version="3.1.1",
     lifespan=lifespan,
 )