feat: add GET endpoints for listing and retrieving agents

- GET /api/v1/agents/ - list all agents (with optional tenant_id filter)
- GET /api/v1/agents/{agent_id} - get specific agent

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

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

app/routes/agents.py

@@ -21,6 +21,7 @@ from app.schemas.agent import (
     AgentRegisterRequestLegacy,
     AgentRegisterResponse,
     AgentRegisterResponseLegacy,
+    AgentResponse,
 )
 
 logger = logging.getLogger(__name__)
@@ -109,6 +110,46 @@ async def validate_agent_token(
 # --- Route handlers (thin controllers) ---
 
 
+@router.get(
+    "/",
+    response_model=list[AgentResponse],
+    summary="List all agents",
+    description="Retrieve all registered agents, optionally filtered by tenant.",
+)
+async def list_agents(
+    db: AsyncSessionDep,
+    tenant_id: uuid.UUID | None = None,
+) -> list[Agent]:
+    """List all agents, optionally filtered by tenant."""
+    query = select(Agent)
+    if tenant_id:
+        query = query.where(Agent.tenant_id == tenant_id)
+    query = query.order_by(Agent.created_at.desc())
+
+    result = await db.execute(query)
+    return list(result.scalars().all())
+
+
+@router.get(
+    "/{agent_id}",
+    response_model=AgentResponse,
+    summary="Get agent by ID",
+    description="Retrieve a specific agent by its UUID.",
+)
+async def get_agent(
+    agent_id: uuid.UUID,
+    db: AsyncSessionDep,
+) -> Agent:
+    """Get a specific agent by ID."""
+    agent = await get_agent_by_id(db, agent_id)
+    if agent is None:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Agent {agent_id} not found",
+        )
+    return agent
+
+
 @router.post(
     "/register",
     response_model=AgentRegisterResponse | AgentRegisterResponseLegacy,