Add screenshots and update gitignore for alpha release

- Fixed gitignore to allow Screenshots/*.png files
- Added all screenshots for README documentation
- Fixed gitignore to be less restrictive with image files
- Includes dashboard, agent, updates, and docker screenshots

aggregator-server/internal/database/queries/agents.go

@@ -45,7 +45,7 @@ func (q *AgentQueries) GetAgentByID(id uuid.UUID) (*models.Agent, error) {
 // UpdateAgentLastSeen updates the agent's last_seen timestamp
 func (q *AgentQueries) UpdateAgentLastSeen(id uuid.UUID) error {
 	query := `UPDATE agents SET last_seen = $1, status = 'online' WHERE id = $2`
-	_, err := q.db.Exec(query, time.Now(), id)
+	_, err := q.db.Exec(query, time.Now().UTC(), id)
 	return err
 }
 
@@ -81,3 +81,77 @@ func (q *AgentQueries) MarkOfflineAgents(threshold time.Duration) error {
 	_, err := q.db.Exec(query, time.Now().Add(-threshold))
 	return err
 }
+
+// GetAgentLastScan gets the last scan time from update events
+func (q *AgentQueries) GetAgentLastScan(id uuid.UUID) (*time.Time, error) {
+	var lastScan time.Time
+	query := `SELECT MAX(created_at) FROM update_events WHERE agent_id = $1`
+	err := q.db.Get(&lastScan, query, id)
+	if err != nil {
+		return nil, err
+	}
+	return &lastScan, nil
+}
+
+// GetAgentWithLastScan gets agent information including last scan time
+func (q *AgentQueries) GetAgentWithLastScan(id uuid.UUID) (*models.AgentWithLastScan, error) {
+	var agent models.AgentWithLastScan
+	query := `
+		SELECT
+			a.*,
+			(SELECT MAX(created_at) FROM update_events WHERE agent_id = a.id) as last_scan
+		FROM agents a
+		WHERE a.id = $1`
+	err := q.db.Get(&agent, query, id)
+	if err != nil {
+		return nil, err
+	}
+	return &agent, nil
+}
+
+// ListAgentsWithLastScan returns all agents with their last scan times
+func (q *AgentQueries) ListAgentsWithLastScan(status, osType string) ([]models.AgentWithLastScan, error) {
+	var agents []models.AgentWithLastScan
+	query := `
+		SELECT
+			a.*,
+			(SELECT MAX(created_at) FROM update_events WHERE agent_id = a.id) as last_scan
+		FROM agents a
+		WHERE 1=1`
+	args := []interface{}{}
+	argIdx := 1
+
+	if status != "" {
+		query += ` AND a.status = $` + string(rune(argIdx+'0'))
+		args = append(args, status)
+		argIdx++
+	}
+	if osType != "" {
+		query += ` AND a.os_type = $` + string(rune(argIdx+'0'))
+		args = append(args, osType)
+		argIdx++
+	}
+
+	query += ` ORDER BY a.last_seen DESC`
+	err := q.db.Select(&agents, query, args...)
+	return agents, err
+}
+
+// DeleteAgent removes an agent and all associated data
+func (q *AgentQueries) DeleteAgent(id uuid.UUID) error {
+	// Start a transaction for atomic deletion
+	tx, err := q.db.Beginx()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	// Delete the agent (CASCADE will handle related records)
+	_, err = tx.Exec("DELETE FROM agents WHERE id = $1", id)
+	if err != nil {
+		return err
+	}
+
+	// Commit the transaction
+	return tx.Commit()
+}