v0.1.19 - Throughput overview & responsive header

- Throughput: new "Throughput Overview" header with Gauge icon and brand-green
  badge icons on each card (Today, This week, 4-week average, Horse Mix, Grain Mix)
- Throughput: inline rolling-range selector (7d / 4w / 6w / 12w, default 4 weeks)
  driving the customer-mix cards; stats window widened to 12 weeks so switching
  range is a pure client-side re-filter
- Throughput: cards collapse to a single even 5-across row on laptop and up,
  with container-query value text that scales to each card's width
- Throughput: date logic pinned to Australian Eastern time (fixes the day-early
  date); This week subtitle shows the Mon-Sun date range
- Throughput: subtler tinted add-form; removed the inline-entry kicker and the
  "Open full form" link
- Topbar: fix cramped laptop header - action toggles no longer wrap above the
  user button; search drops to its own row earlier

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

backend/app/schemas/ordering.py

@@ -238,6 +238,18 @@ class NotificationSettingsUpdate(BaseModel):
     from_email: str | None = None
 
 
+# --- Admin: Xero integration -------------------------------------------------
+
+
+class XeroContactLinkUpsert(BaseModel):
+    """Link a customer to a Xero contact. ``xero_contact_id`` is the Xero
+    ``ContactID`` (or, in stub mode, the deterministic stub id)."""
+
+    xero_contact_id: str = Field(min_length=1, max_length=128)
+    xero_contact_name: str | None = Field(default=None, max_length=255)
+    xero_contact_email: str | None = Field(default=None, max_length=255)
+
+
 # --- Admin: customers & users ------------------------------------------------
 
 _CUSTOMER_STATUSES = {"active", "disabled"}