Add self-service password change, forgot-password flow, and fix admin UI bugs

Users can change their own password from the profile modal, and a
"forgot password" link sends a 15-minute expiring reset link (same
hashed-token pattern as site invites). The forgot-password response is
always generic so it never reveals which emails are registered.

Also fixes two admin-page display bugs found while testing: table row
divider lines that didn't line up across a row (the actions column had
`display: flex` on the <td> itself, breaking it out of normal table-cell
layout -- moved to a child <div>), and the pending-invites list floating
with no visual grouping (now boxed with a label and per-status badges).

frontend/src/components/Modal.css

@@ -48,6 +48,8 @@
 }
 
 .modal input[type='text'],
+.modal input[type='password'],
+.modal input[type='email'],
 .modal textarea {
   width: 100%;
   background: var(--ds-surface-2);
@@ -62,6 +64,8 @@
 }
 
 .modal input[type='text']:focus,
+.modal input[type='password']:focus,
+.modal input[type='email']:focus,
 .modal textarea:focus {
   border-color: var(--ds-accent);
 }
@@ -78,6 +82,18 @@
   margin: -8px 0 var(--sp-3);
 }
 
+.modal-success {
+  color: var(--ds-accent);
+  font-size: 0.82rem;
+  margin: -8px 0 var(--sp-3);
+}
+
+.modal-divider {
+  border: none;
+  border-top: 1px solid var(--ds-border);
+  margin: var(--sp-5) 0 var(--sp-4);
+}
+
 .toggle-row {
   display: flex;
   align-items: center;