feat: Agent zeigt Warnung wenn er nicht den Kunden-Key nutzt

- last_api_key Spalte in agents, wird bei Heartbeat gesetzt
- GetAgentsByCustomer liefert last_api_key mit
- Frontend: rot + Warnsymbol wenn Key abweicht vom Kunden-Agent-Key
- Grau wenn noch kein Heartbeat mit Key-Info

backend/db/postgres.go

@@ -140,6 +140,7 @@ func (d *Database) migrate() error {
 	d.db.Exec("ALTER TABLE agents ADD COLUMN IF NOT EXISTS agent_version TEXT NOT NULL DEFAULT ''")
 	d.db.Exec("ALTER TABLE agents ADD COLUMN IF NOT EXISTS update_requested BOOLEAN NOT NULL DEFAULT FALSE")
 	d.db.Exec("ALTER TABLE agents ADD COLUMN IF NOT EXISTS platform TEXT NOT NULL DEFAULT 'freebsd'")
+	d.db.Exec("ALTER TABLE agents ADD COLUMN IF NOT EXISTS last_api_key TEXT NOT NULL DEFAULT ''")
 
 	// Agent-Firmware Tabelle (Multi-Plattform)
 	d.db.Exec(`CREATE TABLE IF NOT EXISTS agent_firmware (
@@ -627,6 +628,10 @@ func (d *Database) UpdateAgentVersion(id, version string) error {
 	return err
 }
 
+func (d *Database) UpdateAgentAPIKey(id, apiKey string) {
+	d.db.Exec("UPDATE agents SET last_api_key = $1 WHERE id = $2", apiKey, id)
+}
+
 // Update-Request Flag setzen/lesen/loeschen
 func (d *Database) SetUpdateRequest(id string, requested bool) error {
 	_, err := d.db.Exec("UPDATE agents SET update_requested = $1 WHERE id = $2", requested, id)
@@ -1099,7 +1104,7 @@ func (d *Database) UnassignAgentCustomer(agentID string) error {
 }
 
 func (d *Database) GetAgentsByCustomer(customerID int) ([]models.AgentResponse, error) {
-	rows, err := d.db.Query("SELECT id, name, hostname, ip, opnsense_version, registered_at, last_heartbeat, customer_id, agent_version FROM agents WHERE customer_id = $1 ORDER BY name", customerID)
+	rows, err := d.db.Query("SELECT id, name, hostname, ip, opnsense_version, registered_at, last_heartbeat, customer_id, agent_version, last_api_key FROM agents WHERE customer_id = $1 ORDER BY name", customerID)
 	if err != nil {
 		return nil, err
 	}
@@ -1110,7 +1115,7 @@ func (d *Database) GetAgentsByCustomer(customerID int) ([]models.AgentResponse,
 		var a models.Agent
 		var lastHB sql.NullTime
 		var custID sql.NullInt64
-		if err := rows.Scan(&a.ID, &a.Name, &a.Hostname, &a.IP, &a.OPNsenseVersion, &a.RegisteredAt, &lastHB, &custID, &a.AgentVersion); err != nil {
+		if err := rows.Scan(&a.ID, &a.Name, &a.Hostname, &a.IP, &a.OPNsenseVersion, &a.RegisteredAt, &lastHB, &custID, &a.AgentVersion, &a.LastAPIKey); err != nil {
 			return nil, err
 		}
 		if lastHB.Valid {