feat(auth): implement role-based access control (RBAC)

Add roles, permissions, and user_roles tables with default seed data
Protect backend API endpoints with granular permission checks
Add admin UI for managing users, roles, and permissions
Update frontend views to conditionally render actions based on permissions

frontend/src/styles/main.css

@@ -2828,6 +2828,87 @@ button:disabled,
   overflow-wrap: anywhere;
 }
 
+.access-list li {
+  align-items: flex-start;
+}
+
+.access-row,
+.access-modal-heading {
+  min-width: 0;
+  display: grid;
+  gap: 7px;
+}
+
+.access-row strong,
+.access-modal-heading strong {
+  color: var(--ink);
+  overflow-wrap: anywhere;
+}
+
+.permission-groups {
+  display: grid;
+  gap: 14px;
+}
+
+.permission-group {
+  display: grid;
+  gap: 10px;
+  padding: 12px;
+  border: 1px solid var(--line);
+  border-radius: var(--radius-card);
+  background: var(--surface-soft);
+}
+
+.permission-group h3 {
+  margin: 0;
+  color: var(--ink);
+  font-size: 15px;
+}
+
+.permission-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
+  gap: 8px;
+}
+
+.permission-toggle {
+  min-height: 52px;
+  display: grid;
+  grid-template-columns: auto minmax(0, 1fr);
+  gap: 8px;
+  align-items: start;
+  padding: 10px;
+  border: 1px solid var(--line);
+  border-radius: var(--radius-control);
+  background: var(--surface);
+  color: var(--ink-soft);
+  cursor: pointer;
+}
+
+.permission-toggle input {
+  width: 18px;
+  height: 18px;
+  margin-top: 2px;
+  accent-color: var(--pokemon-blue);
+}
+
+.permission-toggle strong,
+.permission-toggle small {
+  display: block;
+  overflow-wrap: anywhere;
+}
+
+.permission-toggle strong {
+  color: var(--ink);
+  font-size: 14px;
+}
+
+.permission-toggle small {
+  margin-top: 2px;
+  color: var(--muted);
+  font-size: 12px;
+}
+
 .chips {
   display: flex;
   flex-wrap: wrap;