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>

server/src/routes/bootstrap.ts

@@ -32,6 +32,7 @@ type InventoryRow = {
   status: string;
   consumed_date: string | null;
   gone_date: string | null;
+  checkout_date: string | null;
   rating: number | null;
   notes: string | null;
 };
@@ -108,6 +109,7 @@ bootstrapRouter.get("/bootstrap", (_req, res) => {
     status: i.status,
     consumedDate: i.consumed_date,
     goneDate: i.gone_date,
+    checkoutDate: i.checkout_date,
     rating: i.rating,
     notes: i.notes,
     audits: (auditsByInventory.get(i.id) ?? []).map((a) => ({