feat(config): allow -1 to represent unlimited upload limits

Introduce support for configuring unlimited upload limits by allowing -1
as a valid value for anonymous and user upload MB limits.

Changes include:
- Added `envMegabytesLimitFloat` and helper functions to parse and validate limits where -1 is allowed.
- Updated validation logic to accept -1 for `AnonymousMaxUploadMB`, `AnonymousDailyUploadMB`, and `UserDailyUploadMB`.
- Added a test case to verify unlimited upload policy behavior.

backend/static/css/50-admin.css

@@ -22,6 +22,7 @@
 }
 
 .metric-card {
+  min-width: 0;
   border: 1px solid var(--border);
   border-radius: var(--radius);
   background: rgba(24, 24, 27, 0.78);
@@ -37,11 +38,26 @@
 
 .metric-card strong {
   display: block;
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
   margin-top: 0.4rem;
   color: var(--foreground);
   font-size: 1.35rem;
 }
 
+.metric-card span {
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.user-edit-metrics {
+  grid-template-columns: repeat(4, minmax(0, 1fr));
+}
+
 .admin-table-card {
   margin-top: 1rem;
 }