fix(demo-seed): stop truncating ingredient/table ids to 36 chars

BuildDemoIngredients/BuildDemoTables built ids as
"{cafeId}_ing_{guid}"[..36]. For a real cafe (32-char hex id) the
first 36 chars are just "{cafeId}_ing" — the unique guid is cut off,
so all 15 ingredients (and all 10 tables) get the SAME id, causing a
primary-key collision on SaveChanges -> 500. cafe_demo_001 has a short
id so the guid survived, which is why the bug only hit real cafes.

The Id columns are text (no length limit), so the truncation served no
purpose. Removed [..36] from both so the full unique id is kept.

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

src/Meezi.API/Services/DemoSeedService.cs

@@ -130,7 +130,10 @@ public class DemoSeedService : IDemoSeedService
         decimal qty, decimal reorder, decimal cost, decimal par) =>
         new()
         {
-            Id = $"{cafeId}_ing_{Guid.NewGuid():N}"[..36],
+            // No [..36] truncation: Id is a text column, and truncating to 36 chars
+            // cuts off the unique guid for real (32-char) café ids → every row gets
+            // the same id → PK collision → 500. Keep the full unique id.
+            Id = $"{cafeId}_ing_{Guid.NewGuid():N}",
             CafeId = cafeId,
             Name = name,
             Unit = unit,
@@ -160,7 +163,9 @@ public class DemoSeedService : IDemoSeedService
         string cafeId, string branchId, string number, int capacity, string floor, int sortOrder) =>
         new()
         {
-            Id = $"{cafeId}_tbl_{Guid.NewGuid():N}"[..36],
+            // No [..36] truncation (see Ingredient above): truncating cuts the guid
+            // for real 32-char café ids → identical ids → PK collision → 500.
+            Id = $"{cafeId}_tbl_{Guid.NewGuid():N}",
             CafeId = cafeId,
             BranchId = branchId,
             Number = number,