feat: implement role-based entry and navigation enhancements

- Replace credential login with Admin/Practitioner role selection
- Add role-switcher toggle in header with automatic reversion for Admin mode
- Implement immediate return to role selection via system logo click
- Integrate role state management into global app state

src/styles/common.css

@@ -229,6 +229,85 @@ body {
   }
 }
 
+/* --- Role Switcher Toggle --- */
+.role-switcher {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  margin-right: 0.5rem;
+  padding: 0 0.75rem;
+  border-right: 1px solid var(--border-color);
+  height: 24px;
+}
+
+.role-label {
+  font-size: 11px;
+  font-weight: 700;
+  color: var(--text-muted);
+  transition: color 0.2s;
+}
+
+.role-label.active {
+  color: var(--primary-color);
+}
+
+.role-label.admin.active {
+  color: var(--color-orange);
+}
+
+/* Toggle Switch Base */
+.switch {
+  position: relative;
+  display: inline-block;
+  width: 34px;
+  height: 18px;
+}
+
+.switch input {
+  opacity: 0;
+  width: 0;
+  height: 0;
+}
+
+.slider {
+  position: absolute;
+  cursor: pointer;
+  top: 0; left: 0; right: 0; bottom: 0;
+  background-color: #ccc;
+  transition: .4s;
+}
+
+.slider:before {
+  position: absolute;
+  content: "";
+  height: 12px;
+  width: 12px;
+  left: 3px;
+  bottom: 3px;
+  background-color: white;
+  transition: .4s;
+}
+
+input:checked + .slider {
+  background-color: var(--color-orange);
+}
+
+input:focus + .slider {
+  box-shadow: 0 0 1px var(--color-orange);
+}
+
+input:checked + .slider:before {
+  transform: translateX(16px);
+}
+
+.slider.round {
+  border-radius: 34px;
+}
+
+.slider.round:before {
+  border-radius: 50%;
+}
+
 /* --- Global Actions & Buttons --- */
 .header-actions {
   display: flex;