feat: salvage Angular developer skill

skills/angular-developer/references/route-guards.md

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+# Route Guards
+
+Route guards control whether a user can navigate to or leave a route.
+
+## Types of Guards
+
+- **`CanActivate`**: Can the user access this route? (e.g., Auth check).
+- **`CanActivateChild`**: Can the user access children of this route?
+- **`CanDeactivate`**: Can the user leave this route? (e.g., Unsaved changes).
+- **`CanMatch`**: Should this route even be considered for matching? (e.g., Feature flags). If it returns `false`, the router continues checking other routes.
+
+## Creating a Guard
+
+Guards are typically functional since Angular 15.
+
+```ts
+export const authGuard: CanActivateFn = (route, state) => {
+  const authService = inject(AuthService);
+  const router = inject(Router);
+
+  if (authService.isLoggedIn()) {
+    return true;
+  }
+
+  // Redirect to login
+  return router.parseUrl('/login');
+};
+```
+
+## Applying Guards
+
+Add them to the route configuration as an array. They execute in order.
+
+```ts
+{
+  path: 'admin',
+  component: Admin,
+  canActivate: [authGuard],
+  canActivateChild: [adminChildGuard],
+  canDeactivate: [unsavedChangesGuard]
+}
+```
+
+## Return Values
+
+- `boolean`: `true` to allow, `false` to block.
+- `UrlTree` or `RedirectCommand`: Redirect to a different route.
+- `Observable` or `Promise`: Resolves to the above types.
+
+## Security Note
+
+**Client-side guards are NOT a substitute for server-side security.** Always verify permissions on the server.