feat: add agent visibility APIs and harden runtime verification

Add Day 4 visibility endpoints and response models, strengthen collaboration/task verification behavior, and patch conversation schema startup migration for agent_state compatibility. Extend backend regression coverage for runtime schemas, verifier behavior, visibility APIs, router auth, and legacy conversation list loading.

backend/app/agents/schemas/event.py

@@ -11,6 +11,18 @@ AgentEventType = Literal[
     "agent.tool.result",
     "agent.verify.started",
     "agent.verify.completed",
+    "agent.created",
+    "agent.spawn.blocked",
+    "agent.message.sent",
+    "agent.message.received",
+    "agent.interrupt.requested",
+    "agent.interrupt.completed",
+    "agent.recovery.started",
+    "agent.recovery.completed",
+    "agent.task.interrupted",
+    "agent.task.recovered",
+    "agent.task.reassigned",
+    "agent.collaboration.budget.updated",
     "agent.error",
 ]
 AgentEventSeverity = Literal["info", "warning", "error"]
@@ -24,5 +36,11 @@ class AgentEvent(BaseModel):
     agent_id: str | None = None
     sub_commander_id: str | None = None
     task_id: str | None = None
+    parent_task_id: str | None = None
+    child_task_id: str | None = None
+    thread_id: str | None = None
+    message_id: str | None = None
+    interrupt_id: str | None = None
+    recovery_id: str | None = None
     payload: dict[str, Any] = Field(default_factory=dict)
     severity: AgentEventSeverity = "info"