docs: reorg and visual refresh (#19765)

- put use cases in main sidebar
- move modules to own sidebar, rename components
- cleanup lcel section
- cleanup guides
- update font, cell highlighting

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

docs/docusaurus.config.js

@@ -149,16 +149,10 @@ const config = {
         logo: {src: "img/brand/wordmark.png", srcDark: "img/brand/wordmark-dark.png"},
         items: [
           {
-            to: "/docs/get_started/introduction",
-            label: "Docs",
+            to: "/docs/modules",
+            label: "Components",
             position: "left",
           },
-          {
-            type: "docSidebar",
-            position: "left",
-            sidebarId: "use_cases",
-            label: "Use cases",
-          },
           {
             type: "docSidebar",
             position: "left",
@@ -166,14 +160,13 @@ const config = {
             label: "Integrations",
           },
           {
-            type: "docSidebar",
-            position: "left",
-            sidebarId: "guides",
+            to: "/docs/guides",
             label: "Guides",
+            position: "left",
           },
           {
             href: "https://api.python.langchain.com",
-            label: "API",
+            label: "API Reference",
             position: "left",
           },
           {
@@ -189,11 +182,6 @@ const config = {
                 to: "/docs/packages",
                 label: "Versioning",
               },
-              {
-                type: "docSidebar",
-                sidebarId: "changelog",
-                label: "Changelog",
-              },
               {
                 to: "/docs/contributing",
                 label: "Contributing",