fix: repair version detection platform query format

- Fix GetLatestVersionByTypeAndArch to separate platform/architecture
- Query now correctly uses platform='linux' and architecture='amd64'
- Resolves UI showing 'no packages available' despite updates existing

aggregator-server/internal/models/agent_update.go

@@ -23,10 +23,11 @@ type AgentUpdatePackage struct {
 
 // AgentUpdateRequest represents a request to update an agent
 type AgentUpdateRequest struct {
-	AgentID   uuid.UUID `json:"agent_id" binding:"required"`
+	AgentID   uuid.UUID `json:"agent_id,omitempty"`         // Optional when agent ID is in URL path
 	Version   string    `json:"version" binding:"required"`
 	Platform  string    `json:"platform" binding:"required"`
 	Scheduled *string   `json:"scheduled_at,omitempty"`
+	Nonce     string    `json:"nonce" binding:"required"` // Required security nonce to prevent replay attacks
 }
 
 // BulkAgentUpdateRequest represents a bulk update request