Add schemas documentation to core concepts page

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bchapuis

apps/app/src/pages/docs/concepts-page.tsx

@@ -87,6 +87,13 @@ export function DocsOverviewPage() {
           during execution:
         </p>
         <ul>
+          <li>
+            <strong>Schemas:</strong> Reusable definitions that describe the
+            shape of records used in your workflows. Each schema has a name,
+            description, and a set of typed fields. Use schemas to validate and
+            enforce consistent data structures across nodes, ensuring that
+            inputs and outputs conform to expected formats.
+          </li>
           <li>
             <strong>Databases:</strong> Managed SQLite databases for storing and
             querying structured data. Workflows can read from and write to