feat: add websockets as main dependency for @app.websocket decorator

The @app.websocket decorator requires the websockets library for uvicorn
to handle WebSocket upgrades. Moving websockets from dev dependencies to
main dependencies ensures customers get it automatically when installing
bedrock-agentcore.

This prevents the error:
'WARNING: No supported WebSocket library detected'

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: Abishek Kumar

pyproject.toml

@@ -33,6 +33,7 @@ dependencies = [
     "starlette>=0.46.2",
     "typing-extensions>=4.13.2,<5.0.0",
     "uvicorn>=0.34.2",
+    "websockets>=12.0",
     "pre-commit>=4.2.0",
 ]