feat(plan): add hard-delete for categories (blocked when in use)

DELETE /plan/categories/:id now hard-deletes the row, guarded: refuses when any live entry/override uses the key (suggests hide instead) and keeps >=1 active category. Modal gains a per-row Smazat with inline confirm. Hiding stays via PATCH is_active.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/__tests__/planCategory.test.ts

@@ -5,6 +5,7 @@ import {
   createPlanCategory,
   updatePlanCategory,
   deactivatePlanCategory,
+  deletePlanCategory,
   isCategoryKeyActive,
   slugifyCategory,
 } from "../services/planCategory.service";
@@ -83,4 +84,46 @@ describe("plan category service", () => {
     await deactivatePlanCategory(res.data.id);
     expect(await isCategoryKeyActive("test_deact_zz")).toBe(false);
   });
+
+  it("hard-deletes an unused category", async () => {
+    const res = await createPlanCategory({
+      label: "Test Del ZZ",
+      color: "#dddddd",
+    });
+    if ("error" in res) throw new Error(res.error);
+    const del = await deletePlanCategory(res.data.id);
+    expect("data" in del).toBe(true);
+    const stillThere = await prisma.plan_categories.findUnique({
+      where: { id: res.data.id },
+    });
+    expect(stillThere).toBeNull();
+  });
+
+  it("refuses to hard-delete a category in use", async () => {
+    const res = await createPlanCategory({
+      label: "Test InUse ZZ",
+      color: "#eeeeee",
+    });
+    if ("error" in res) throw new Error(res.error);
+    created.push(res.data.id);
+    const user = await prisma.users.findFirst({ select: { id: true } });
+    if (!user) throw new Error("no user in test DB");
+    const entry = await prisma.work_plan_entries.create({
+      data: {
+        user_id: user.id,
+        date_from: new Date("2026-06-10T00:00:00.000Z"),
+        date_to: new Date("2026-06-10T00:00:00.000Z"),
+        category: res.data.key,
+        note: "test in-use",
+        created_by: user.id,
+      },
+    });
+    try {
+      const del = await deletePlanCategory(res.data.id);
+      expect("error" in del).toBe(true);
+      if ("error" in del) expect(del.status).toBe(409);
+    } finally {
+      await prisma.work_plan_entries.delete({ where: { id: entry.id } });
+    }
+  });
 });