feat(print): route print jobs through a local agent, fall back to TCP

Phase 2. NetworkPrinterService now builds the ESC/POS bytes (as before) and
dispatches them via a new router: if the receipt/kitchen/station printer is mapped
to a PrintDevice whose agent is online, the bytes are sent to that agent over the
hub and we await its ack; otherwise it falls back to a direct TCP connection (raw
IP), so existing on-prem/reachable printers keep working unchanged. Adds nullable
mapping columns Branch.ReceiptPrintDeviceId / KitchenPrintDeviceId and
KitchenStation.PrintDeviceId (additive migration), plus TestPrintDeviceAsync for
testing an agent printer. The cloud can now reach LAN/USB printers it never could.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Meezi.Infrastructure/Data/Migrations/AppDbContextModelSnapshot.cs

@@ -155,6 +155,9 @@ namespace Meezi.Infrastructure.Data.Migrations
                     b.Property<bool>("IsActive")
                         .HasColumnType("boolean");
 
+                    b.Property<string>("KitchenPrintDeviceId")
+                        .HasColumnType("text");
+
                     b.Property<string>("KitchenPrinterIp")
                         .HasMaxLength(45)
                         .HasColumnType("character varying(45)");
@@ -192,6 +195,9 @@ namespace Meezi.Infrastructure.Data.Migrations
                         .HasMaxLength(500)
                         .HasColumnType("character varying(500)");
 
+                    b.Property<string>("ReceiptPrintDeviceId")
+                        .HasColumnType("text");
+
                     b.Property<string>("ReceiptPrinterIp")
                         .HasMaxLength(45)
                         .HasColumnType("character varying(45)");
@@ -1313,6 +1319,9 @@ namespace Meezi.Infrastructure.Data.Migrations
                         .HasMaxLength(100)
                         .HasColumnType("character varying(100)");
 
+                    b.Property<string>("PrintDeviceId")
+                        .HasColumnType("text");
+
                     b.Property<string>("PrinterIp")
                         .HasMaxLength(45)
                         .HasColumnType("character varying(45)");