Fix chpasswd path on NixOS, add password toggle/hints/validation in change-password form

Agent-Logs-Url: https://github.com/naturallaw777/staging_alpha/sessions/de03873d-5cdb-4929-bd4a-4d306916b525

Co-authored-by: naturallaw777 <99053422+naturallaw777@users.noreply.github.com>

app/sovran_systemsos_web/static/css/security.css

@@ -40,3 +40,68 @@
 .security-inline-link:hover {
   background-color: rgba(180, 100, 0, 0.22);
 }
+
+/* ── System change-password form extras ──────────────────────────── */
+
+.sys-chpw-header {
+  margin-bottom: 14px;
+}
+
+.sys-chpw-title {
+  font-size: 1rem;
+  font-weight: 600;
+  color: var(--text-primary);
+  margin-bottom: 4px;
+}
+
+.sys-chpw-desc {
+  font-size: 0.82rem;
+  color: var(--text-secondary);
+  line-height: 1.5;
+}
+
+.pw-input-wrap {
+  position: relative;
+  display: flex;
+  align-items: center;
+}
+
+.pw-input-wrap .matrix-form-input {
+  padding-right: 2.4rem;
+  width: 100%;
+}
+
+.pw-toggle-btn {
+  position: absolute;
+  right: 6px;
+  background: none;
+  border: none;
+  cursor: pointer;
+  font-size: 1rem;
+  padding: 2px 4px;
+  line-height: 1;
+  color: var(--text-secondary);
+  opacity: 0.75;
+  transition: opacity 0.15s;
+}
+
+.pw-toggle-btn:hover {
+  opacity: 1;
+}
+
+.pw-hint {
+  font-size: 0.76rem;
+  color: var(--text-secondary);
+  margin-top: 4px;
+}
+
+.pw-credentials-note {
+  font-size: 0.78rem;
+  color: #c97a00;
+  background-color: rgba(180, 100, 0, 0.10);
+  border-left: 2px solid #c97a00;
+  border-radius: 4px;
+  padding: 7px 10px;
+  margin-bottom: 12px;
+  line-height: 1.5;
+}