Add checkout/custody feature for tracking items in personal possession

Items can now be checked out of their bin into "my custody" and later
checked back in or marked consumed. Adds checkout/checkin API endpoints,
a My Custody sidebar page, CheckoutFlow and CheckinFlow modals, and
updates ProductDetail, Inventory, ConsumeFlow, and MarkGoneFlow to
handle the new checked-out status. Bulk items prompt for remaining
weight on check-in.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/types.ts

@@ -1,4 +1,4 @@
-export type ProductStatus = "active" | "consumed" | "gone";
+export type ProductStatus = "active" | "consumed" | "gone" | "checked-out";
 export type ProductKind = "bulk" | "discrete";
 export type AuditMode = "weigh" | "estimate" | "presence";
 
@@ -46,6 +46,7 @@ export interface InventoryItem {
   status: ProductStatus;
   consumedDate: string | null;
   goneDate: string | null;
+  checkoutDate: string | null;
   rating: number | null;
   notes: string | null;
   audits: Audit[];
@@ -197,13 +198,13 @@ export const helpers = {
     return Math.floor((+new Date(today) - +new Date(last)) / 86_400_000);
   },
   auditOverdue(p: Item, today = TODAY_STR): boolean {
-    if (p.status !== "active") return false;
+    if (p.status !== "active" && p.status !== "checked-out") return false;
     const cfg = TYPES.find((t) => t.id === p.type);
     if (!cfg) return false;
     return this.daysSinceCheck(p, today) >= cfg.cadenceDays;
   },
   estimatedRemaining(p: Item, today = TODAY_STR): number {
-    if (p.status !== "active") return 0;
+    if (p.status !== "active" && p.status !== "checked-out") return 0;
     if (p.kind === "discrete") {
       return p.countLastAudit ?? p.countOriginal;
     }