feat: add Jarvis agent verification foundation

Add Day 1 agent runtime foundations with task and event schemas, verifier support, capability metadata, graph event tracing, and regression coverage while preserving the direct execution path.

backend/app/agents/schemas/event.py

@@ -0,0 +1,28 @@
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from typing import Any, Literal
+
+from pydantic import BaseModel, Field
+
+
+AgentEventType = Literal[
+    "agent.tool.start",
+    "agent.tool.result",
+    "agent.verify.started",
+    "agent.verify.completed",
+    "agent.error",
+]
+AgentEventSeverity = Literal["info", "warning", "error"]
+
+
+class AgentEvent(BaseModel):
+    event_id: str
+    event_type: AgentEventType
+    timestamp: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+    conversation_id: str | None = None
+    agent_id: str | None = None
+    sub_commander_id: str | None = None
+    task_id: str | None = None
+    payload: dict[str, Any] = Field(default_factory=dict)
+    severity: AgentEventSeverity = "info"