feat(sidebar): add visible database filters

src/lib/visibleDatabases.ts

@@ -0,0 +1,19 @@
+export function visibleDatabaseFilterIsEnabled(visibleDatabases: string[] | undefined): boolean {
+  return Array.isArray(visibleDatabases);
+}
+
+export function filterVisibleDatabaseNames(databaseNames: string[], visibleDatabases: string[] | undefined): string[] {
+  if (!visibleDatabaseFilterIsEnabled(visibleDatabases)) return databaseNames;
+  const visible = new Set(visibleDatabases);
+  return databaseNames.filter((name) => visible.has(name));
+}
+
+export function normalizeVisibleDatabaseSelection(selectedNames: string[], databaseNames: string[]): string[] {
+  const available = new Set(databaseNames);
+  const seen = new Set<string>();
+  return selectedNames.filter((name) => {
+    if (!available.has(name) || seen.has(name)) return false;
+    seen.add(name);
+    return true;
+  });
+}