fix: update docs redirect to use lowercase index.md

Changed DocsHome redirect from /docs/INDEX.md to /docs/index.md
to match the renamed file.

internal/docs/http_handler.go

@@ -213,7 +213,7 @@ func (h *HTTPHandler) showLegacyAPIEndpoint(c echo.Context, endpointPath string,
 
 // DocsHome redirects to the documentation index
 func (h *HTTPHandler) DocsHome(c echo.Context) error {
-	return c.Redirect(http.StatusFound, "/docs/INDEX.md")
+	return c.Redirect(http.StatusFound, "/docs/index.md")
 }
 
 // APIHome shows the API documentation home page