Let admins create and delete users in Benutzerverwaltung, modernize list

Wire up two previously-unwired stored procedures for the usr module:
- fis_admin_createUserAccount gained the missing @authaccount +
  intranet_admin auth gate, a duplicate-email check, and now returns
  the (possibly auto-generated) password so it can be emailed to the
  new user, mirroring fis_admin_resetUserPassword's pattern.
- fis_admin_delUserAccount gained the same missing auth gate plus a
  guard against an admin deleting their own account.

New /do/usr/create and /do/usr/delete endpoints in
IntranetController.AdminUsers.cs, a "Neuer Benutzer" button and a
"Benutzer löschen" ribbon action in fis.usr.js, and unit tests for the
new welcome-email content (BuildWelcomeEmail).

Also restyle the user list (fis.usr.scss) from a plain bordered table
to a card-style row grid with avatar-initial badges and status pills,
matching the Admin dashboard's visual language.

Documented as ADR 0020 and in the admin-user-management concept doc.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Fuchs/js/intranet/modules/fis.usr.scss

@@ -1,33 +1,78 @@
 .usrfrm {
-    > table {
-        border-collapse: collapse;
-        margin: 2rem;
+    padding: 1.5rem 2rem;
 
-        th {
-            padding: 0.2rem 0.35rem;
-            border: 1px solid #CCC;
+    .usr_grid {
+        border: 1px solid #e2e2e2;
+        border-radius: 0.5rem;
+        background: #fff;
+        box-shadow: 0 1px 3px rgba(50, 50, 50, 0.1);
+        overflow: hidden;
+    }
+
+    .usr_row {
+        display: grid;
+        grid-template-columns: 2.75rem 1.6fr 1.8fr 8rem;
+        align-items: center;
+        gap: 0.75rem;
+        padding: 0.55rem 1rem;
+        border-bottom: 1px solid #eee;
+
+        &:last-child { border-bottom: none; }
+    }
+
+    .usr_row_hd {
+        background: $fuchs_blau;
+        color: #fff;
+        font-weight: bold;
+        font-size: 0.85rem;
+        text-transform: uppercase;
+        letter-spacing: 0.02em;
+        padding: 0.5rem 1rem;
+    }
+
+    .usr_row:not(.usr_row_hd) {
+        cursor: pointer;
+        transition: background-color 0.12s ease-in-out;
+
+        &:hover { background-color: #f3f6fb; }
+
+        &.selected {
+            background-color: rgba($fuchs_akzent, 0.12);
+            box-shadow: inset 3px 0 0 $fuchs_akzent;
         }
+    }
 
-        td {
-            padding: 0.2rem 0.35rem;
-            border: 1px solid #CCC;
-        }
+    .usr_avatar {
+        width: 2.1rem;
+        height: 2.1rem;
+        border-radius: 50%;
+        background: $fuchs_blau;
+        color: #fff;
+        font-size: 0.78rem;
+        font-weight: bold;
+        display: flex;
+        align-items: center;
+        justify-content: center;
+    }
 
-        tr {
-            cursor: pointer;
+    .usr_col_name { font-weight: 600; color: #222; }
+    .usr_col_email { color: #555; overflow-wrap: anywhere; }
 
-            &:nth-child(2n+1) td {
-                background-color: #EEE;
-            }
+    .usr_pill {
+        display: inline-block;
+        padding: 0.1rem 0.6rem;
+        border-radius: 1rem;
+        font-size: 0.78rem;
+        font-weight: bold;
+        white-space: nowrap;
+    }
+    .usr_pill_on { background: #e2f3da; color: #2f6d18; }
+    .usr_pill_off { background: #ececec; color: #777; }
 
-            &:hover td {
-                background-color: #f3f6fb;
-            }
-
-            &.selected td {
-                background-color: lightblue;
-            }
-        }
+    .usr_empty {
+        padding: 1.5rem 1rem;
+        text-align: center;
+        color: #777;
     }
 
     .usr_err {
@@ -37,6 +82,19 @@
     }
 }
 
+@media (max-width: 640px) {
+    .usrfrm {
+        padding: 0.75rem;
+
+        .usr_row { grid-template-columns: 2.25rem 1fr; grid-template-areas: "avatar name" "avatar email" "avatar status"; }
+        .usr_row_hd { display: none; }
+        .usr_avatar { grid-area: avatar; }
+        .usr_col_name { grid-area: name; }
+        .usr_col_email { grid-area: email; font-size: 0.85rem; }
+        .usr_col_status { grid-area: status; }
+    }
+}
+
 .usr_groups_dlg {
     padding: 0.25rem 0;