feat(pricing): add workspace user rates and price units

apps/workspaces/models.py

@@ -75,3 +75,57 @@ class WorkspaceMembership(BaseModel):
 
     def __str__(self):
         return f"{self.user} @ {self.workspace}"
+
+
+class PriceUnit(BaseModel):
+    code = models.CharField(max_length=8, unique=True)
+    name = models.CharField(max_length=64)
+    local_name = models.CharField(max_length=64, blank=True)
+    symbol = models.CharField(max_length=16, blank=True)
+
+    class Meta:
+        db_table = "price_unit"
+        ordering = ("code",)
+        indexes = [
+            models.Index(fields=["code"], name="price_unit_code_idx"),
+        ]
+
+    def __str__(self):
+        return self.code
+
+
+class WorkspaceUserRate(BaseModel):
+    workspace = models.ForeignKey(
+        Workspace,
+        on_delete=models.CASCADE,
+        related_name="user_rates",
+    )
+    user = models.ForeignKey(
+        User,
+        on_delete=models.CASCADE,
+        related_name="workspace_rates",
+    )
+    hourly_rate = models.DecimalField(
+        max_digits=10,
+        decimal_places=2,
+    )
+    currency = models.CharField(
+        max_length=3,
+        default="USD",
+    )
+    effective_from = models.DateTimeField()
+
+    class Meta:
+        db_table = "workspace_user_rate"
+        ordering = ("-effective_from",)
+        constraints = [
+            models.UniqueConstraint(
+                fields=["workspace", "user"],
+                name="unique_workspace_user_rate",
+                condition=models.Q(is_deleted=False),
+            )
+        ]
+        indexes = [
+            models.Index(fields=["workspace"], name="wur_workspace_idx"),
+            models.Index(fields=["user"], name="wur_user_idx"),
+        ]