Rename AssetItemStatus 'assigned' to 'in_use'

'assigned' implied a specific person always holds the item, but
createAssignment() only requires status=in_stock to hand something out --
the status value itself never guaranteed a matching Assignment row exists.
~158 of the 613 real-imported assets carry this status with no Assignment
at all (shared/unowned equipment like meeting-room gear), so "assigned"
was actively misleading for them. 'in_use' doesn't carry that implication.

DB: `ALTER TYPE "AssetItemStatus" RENAME VALUE 'assigned' TO 'in_use'`
(hand-written migration -- runs cleanly, no data migration needed, every
existing row's status just reads under the new name). Renamed across:
schema.prisma enum, src/lib/assets.ts (type union + IMPORT_STATUS_MAP,
which keeps an `assigned` key mapped to `in_use` for backward-compat with
pre-2026-08-25 exports/CSVs), src/lib/assignments.ts (the literal status
value createAssignment() sets), src/app/assets/page.tsx + api/assets/
route.ts (filter dropdown + validStatuses), src/app/maintenance-records/
page.tsx (its own copy of the status list for the "close" targetStatus
picker). maintenance-records.ts itself needed no logic change -- its
closeableTargetStatusValues was already just ["in_stock", "retired"],
"assigned" was never a valid close target, only mentioned in comments
(updated for accuracy).

Also fixes a real regression found while verifying this: tests/
assets.test.ts (a pre-existing, properly-reviewed test file, not written
this session) broke 2 commits ago when GET /api/assets's signature and
response shape changed for pagination -- it still called GET() with no
Request and expected a bare array. tsc didn't catch this until now
because this container has no dev bind mount (Dockerfile is COPY-based,
`docker exec` only reflects the last build) -- see the
ubi-dan-itam-docker-no-bind-mount memory note. Added a getRequest()
helper and updated assertions to the {items, total} shape.

Verified by actually rebuilding and running the full suite fresh (not
just tsc/lint smoke checks): 369/369 tests pass, including
assignments.test.ts and maintenance-records.test.ts, which this rename
touches directly. tsc/lint clean against the rebuilt image. Migration
applied to the real DB, data verified intact (542 in_use + 71 in_stock =
613, matches pre-rename counts exactly).

tests/assignments.test.ts

@@ -72,7 +72,7 @@ async function createTestModelId(): Promise<string> {
 }
 
 let serialCounter = 0;
-function createTestAssetItem(overrides: { modelId: string; status?: "in_stock" | "assigned" | "repair" | "retired" }) {
+function createTestAssetItem(overrides: { modelId: string; status?: "in_stock" | "in_use" | "repair" | "retired" }) {
   serialCounter += 1;
   return prisma.assetItem.create({
     data: {
@@ -223,7 +223,7 @@ describe("validateReturnAssignmentInput", () => {
 });
 
 describe("createAssignment", () => {
-  it("assigns an in_stock AssetItem, flips its status to assigned", async () => {
+  it("assigns an in_stock AssetItem, flips its status to in_use", async () => {
     const employee = await createTestEmployee();
     const modelId = await createTestModelId();
     const assetItem = await createTestAssetItem({ modelId });
@@ -236,10 +236,10 @@ describe("createAssignment", () => {
     expect(created.value.returned_at).toBeNull();
 
     const updatedItem = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
-    expect(updatedItem.status).toBe("assigned");
+    expect(updatedItem.status).toBe("in_use");
   });
 
-  it.each(["repair", "retired", "assigned"] as const)(
+  it.each(["repair", "retired", "in_use"] as const)(
     "rejects assigning an AssetItem whose status is %s",
     async (status) => {
       const employee = await createTestEmployee();
@@ -312,7 +312,7 @@ describe("createAssignment", () => {
     expect(second.value.employee_id).toBe(employee2.id);
 
     const updatedItem = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
-    expect(updatedItem.status).toBe("assigned");
+    expect(updatedItem.status).toBe("in_use");
   });
 
   it("returns a clean error when assetItemId doesn't reference an existing asset item", async () => {
@@ -434,7 +434,7 @@ describe("createAssignment", () => {
     expect(failed).toHaveLength(1);
 
     const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
-    expect(item.status).toBe("assigned");
+    expect(item.status).toBe("in_use");
 
     const activeAssignments = await prisma.assignment.findMany({
       where: { assetItemId: assetItem.id, returnedAt: null },
@@ -545,7 +545,7 @@ describe("returnAssignment", () => {
 });
 
 describe("transferAssignment", () => {
-  it("transfers an AssetItem assignment to a new employee, keeping status assigned throughout", async () => {
+  it("transfers an AssetItem assignment to a new employee, keeping status in_use throughout", async () => {
     const employee1 = await createTestEmployee({ name: "Employee 1" });
     const employee2 = await createTestEmployee({ name: "Employee 2" });
     const modelId = await createTestModelId();
@@ -562,11 +562,11 @@ describe("transferAssignment", () => {
     expect(transferred.value.asset_item_id).toBe(assetItem.id);
     expect(transferred.value.returned_at).toBeNull();
 
-    // The AssetItem must remain "assigned" throughout the transfer — never
+    // The AssetItem must remain "in_use" throughout the transfer — never
     // flipped to in_stock mid-way (that's the whole point of doing this in
     // one transaction rather than a separate return + create).
     const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
-    expect(item.status).toBe("assigned");
+    expect(item.status).toBe("in_use");
 
     const original = await prisma.assignment.findUniqueOrThrow({ where: { id: created.value.id } });
     expect(original.returnedAt).not.toBeNull();
@@ -658,7 +658,7 @@ describe("transferAssignment", () => {
     const original = await prisma.assignment.findUniqueOrThrow({ where: { id: created.value.id } });
     expect(original.returnedAt).toBeNull();
     const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
-    expect(item.status).toBe("assigned");
+    expect(item.status).toBe("in_use");
   });
 });
 
@@ -898,7 +898,7 @@ describe("PATCH /api/assignments/[id]", () => {
     expect(body.returned_at).toBeNull();
 
     const item = await prisma.assetItem.findUniqueOrThrow({ where: { id: assetItem.id } });
-    expect(item.status).toBe("assigned");
+    expect(item.status).toBe("in_use");
   });
 
   it("rejects a body with both employeeId and returnedAt with a mutual-exclusivity 400", async () => {