docs: enhance documentation with new modes and plugins

- Updated documentation to include new modes for configuring bknd (UI-only, Code-only, Hybrid).
- Introduced `syncSecrets` plugin example in the extending plugins documentation.
- Added `react-icons` dependency to package.json and package-lock.json.
- Enhanced various documentation pages with icons and improved content structure.

docs/package-lock.json

@@ -23,6 +23,7 @@
         "next": "15.3.5",
         "react": "^19.1.0",
         "react-dom": "^19.1.0",
+        "react-icons": "^5.5.0",
         "tailwind-merge": "^3.3.1",
         "twoslash": "^0.3.2"
       },
@@ -10352,6 +10353,15 @@
         "react": "^16.8.0 || ^17 || ^18 || ^19"
       }
     },
+    "node_modules/react-icons": {
+      "version": "5.5.0",
+      "resolved": "https://registry.npmjs.org/react-icons/-/react-icons-5.5.0.tgz",
+      "integrity": "sha512-MEFcXdkP3dLo8uumGI5xN3lDFNsRtrjbOEKDLD7yv76v4wpnEq2Lt2qeHaQOr34I/wPN3s3+N08WkQ+CW37Xiw==",
+      "license": "MIT",
+      "peerDependencies": {
+        "react": "*"
+      }
+    },
     "node_modules/react-is": {
       "version": "16.13.1",
       "resolved": "https://registry.npmjs.org/react-is/-/react-is-16.13.1.tgz",