Add shop, POS sync, event ticketing, and shipping catalog apps.

Clients can run in-house retail without Shopify while keeping the same
Docker/Django/Postgres stack and data-ownership promise. Closes #5.

site/pos_sync/models.py

@@ -0,0 +1,61 @@
+from django.db import models
+
+from core.models import TimeStampedModel, UUIDPrimaryKeyModel
+
+
+class POSConnection(UUIDPrimaryKeyModel, TimeStampedModel):
+    class Provider(models.TextChoices):
+        GENERIC = "generic", "Generic REST"
+        SQUARE = "square", "Square"
+        LIGHTSPEED = "lightspeed", "Lightspeed"
+        BINDERPOS = "binderpos", "BinderPOS"
+        CRYSTALCOMMERCE = "crystalcommerce", "CrystalCommerce"
+
+    name = models.CharField(max_length=120)
+    provider = models.CharField(
+        max_length=32, choices=Provider.choices, default=Provider.GENERIC
+    )
+    api_base_url = models.URLField(blank=True)
+    api_token = models.CharField(max_length=255, blank=True)
+    webhook_secret = models.CharField(max_length=255, blank=True)
+    is_active = models.BooleanField(default=True)
+
+    class Meta:
+        ordering = ["name"]
+
+    def __str__(self) -> str:
+        return self.name
+
+
+class SyncEvent(UUIDPrimaryKeyModel, TimeStampedModel):
+    class Direction(models.TextChoices):
+        INBOUND = "inbound", "POS → site"
+        OUTBOUND = "outbound", "Site → POS"
+
+    class Status(models.TextChoices):
+        PENDING = "pending", "Pending"
+        DONE = "done", "Done"
+        FAILED = "failed", "Failed"
+
+    connection = models.ForeignKey(
+        POSConnection,
+        null=True,
+        blank=True,
+        on_delete=models.SET_NULL,
+        related_name="events",
+    )
+    direction = models.CharField(max_length=16, choices=Direction.choices)
+    status = models.CharField(
+        max_length=16, choices=Status.choices, default=Status.PENDING
+    )
+    sku = models.CharField(max_length=64)
+    quantity = models.IntegerField(default=0)
+    external_id = models.CharField(max_length=255, blank=True)
+    payload = models.JSONField(default=dict, blank=True)
+    error = models.TextField(blank=True)
+
+    class Meta:
+        ordering = ["-created_at"]
+
+    def __str__(self) -> str:
+        return f"{self.direction} {self.sku} × {self.quantity} · {self.status}"