refactor(docs): migrate existing content to v1 legacy structure

- Move all existing docs content (concepts, project, solution) to /docs/v1/
- Add legacy banner component to warn users about archived documentation
- Create v1 index page with legacy notice and redirect guidance
- Implement automatic banner display for all v1 paths
- Preserve all original content for reference during migration

This enables incremental content migration while maintaining access to
original documentation.

content/en/docs/v1/_index.md

@@ -0,0 +1,13 @@
+---
+title: "Documentation (v1 - Legacy)"
+linkTitle: "v1 (Legacy)"
+weight: 100
+description: >
+  Legacy documentation - archived version of the original content.
+---
+
+{{% alert title="Note" color="warning" %}}
+This is the legacy documentation (v1). For the latest version, please visit the [current documentation](/docs/).
+{{% /alert %}}
+
+This section contains the original documentation that is being migrated to a new structure.