Add FastAPI backend with agent system

backend/app/schemas/agent.py

@@ -0,0 +1,55 @@
+from pydantic import BaseModel
+
+
+class AgentCreate(BaseModel):
+    name: str
+    role: str
+    description: str | None = None
+    system_prompt: str
+
+
+class AgentOut(BaseModel):
+    id: str
+    name: str
+    role: str
+    description: str | None
+    is_active: bool
+    is_default: bool
+
+    model_config = {"from_attributes": True}
+
+
+class AgentMessageOut(BaseModel):
+    id: str
+    agent_id: str
+    conversation_id: str
+    role: str
+    content: str
+
+    model_config = {"from_attributes": True}
+
+
+class AgentStats(BaseModel):
+    agent_id: str
+    call_count: int
+    current_task: str | None
+    status: str  # active | idle | disabled
+
+
+class AgentConfigUpdate(BaseModel):
+    name: str | None = None
+    description: str | None = None
+    system_prompt: str | None = None
+    enabled: bool | None = None
+
+
+class AgentConfigOut(BaseModel):
+    id: str
+    name: str
+    role: str
+    description: str | None
+    system_prompt: str
+    enabled: bool
+    is_active: bool
+
+    model_config = {"from_attributes": True}