f-21: refactor: add dispatcher layer for MQTT migration

Introduce internal/dispatcher package with a Command interface and typed
commands (CreateVPC, DeleteVPC, CreateSubnet, DeleteSubnet). The API
handlers now call dispatcher.Dispatch() instead of enqueuing closures
directly, decoupling transport (HTTP today, MQTT tomorrow) from execution.

Signed-off-by: GnomeZworc <nicolas.boufidjeline@g3e.fr>

internal/dispatcher/subnet_commands.go

@@ -0,0 +1,26 @@
+package dispatcher
+
+import "github.com/dgraph-io/badger/v4"
+
+type CreateSubnetCommand struct {
+	Name      string
+	VPC       string
+	VxlanID   int
+	LocalIP   string
+	GatewayIP string
+	CIDR      string
+}
+
+func (c CreateSubnetCommand) Execute(db *badger.DB) error {
+	// TODO: brancher internal/subnet/create.go
+	return nil
+}
+
+type DeleteSubnetCommand struct {
+	Name string
+}
+
+func (c DeleteSubnetCommand) Execute(db *badger.DB) error {
+	// TODO: brancher internal/subnet/delete.go
+	return nil
+}