feat: initialize interactive live-stream game backend MVP

- Add FastAPI backend with WebSocket support
- Implement ConnectionManager for client connections
- Create GameEngine with async game loop (2s tick)
- Add RuleBasedAgent for keyword-based responses
- Define Pydantic schemas for GameEvent protocol
- Create debug frontend dashboard for testing

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

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

backend/app/schemas.py

@@ -0,0 +1,53 @@
+"""
+Pydantic models for the JSON protocol.
+Defines standardized structures for game events and messages.
+"""
+
+from enum import Enum
+from typing import Any
+from pydantic import BaseModel, Field
+import time
+
+
+class EventType(str, Enum):
+    """Enumeration of all possible game event types."""
+    COMMENT = "comment"
+    AGENT_RESPONSE = "agent_response"
+    TICK = "tick"
+    SYSTEM = "system"
+    ERROR = "error"
+
+
+class GameEvent(BaseModel):
+    """
+    Standardized game event structure for WebSocket communication.
+
+    Attributes:
+        event_type: The type of event (comment, agent_response, tick, etc.)
+        timestamp: Unix timestamp when the event was created
+        data: Arbitrary payload data for the event
+    """
+    event_type: str = Field(..., description="Type of the game event")
+    timestamp: float = Field(default_factory=time.time, description="Unix timestamp")
+    data: dict[str, Any] = Field(default_factory=dict, description="Event payload")
+
+    class Config:
+        json_schema_extra = {
+            "example": {
+                "event_type": "comment",
+                "timestamp": 1704067200.0,
+                "data": {"user": "User123", "message": "Attack!"}
+            }
+        }
+
+
+class ClientMessage(BaseModel):
+    """
+    Message structure for client-to-server communication.
+
+    Attributes:
+        action: The action the client wants to perform
+        payload: Data associated with the action
+    """
+    action: str = Field(..., description="Action to perform")
+    payload: dict[str, Any] = Field(default_factory=dict, description="Action payload")