Project chronological date: YMD admin, month/year public, sort/recent

- Serialize and save project.date as date-only YYYY-MM-DD (no TZ drift)
- Admin label + hint; projects list shows Date column
- Home Recent and portfolio date sort use project.date (nulls last)
- Public display stays month+year / year-only via safe formatters

client/src/styles/global.scss

@@ -181,6 +181,15 @@ h4 {
     min-height: 120px;
     resize: vertical;
   }
+
+  &__hint {
+    margin: 0;
+    font-size: 0.78rem;
+    color: var(--text-dim);
+    text-transform: none;
+    letter-spacing: 0;
+    line-height: 1.35;
+  }
 }
 
 .badge {