[NEB-210] Nebula: Add image upload (#6995)

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## PR-Codex overview
This PR introduces image upload functionality within the chat application, enhancing user interaction by allowing users to send images along with text messages. It also includes updates to various components to support this feature.

### Detailed summary
- Added `allowImageUpload` prop to multiple components.
- Introduced `ImageUploadButton` for image selection.
- Modified `ChatBar` to handle image uploads and message composition.
- Updated `FloatingChatContentLoggedIn`, `ChatPageContent`, and `EmptyStateChatPageContent` to accommodate new props.
- Enhanced `NebulaImage` for displaying uploaded images.
- Implemented image preview and removal functionality in `ChatBar`.

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Author: MananTank

apps/dashboard/src/@/components/ui/image-upload-button.tsx

@@ -0,0 +1,44 @@
+"use client";
+
+import { Button } from "@/components/ui/button";
+import type React from "react";
+import { useRef } from "react";
+
+interface ImageUploadProps {
+  value: File | undefined;
+  onChange?: (files: File[]) => void;
+  children?: React.ReactNode;
+  variant?: React.ComponentProps<typeof Button>["variant"];
+  className?: string;
+  multiple?: boolean;
+}
+
+export function ImageUploadButton(props: ImageUploadProps) {
+  const fileInputRef = useRef<HTMLInputElement>(null);
+
+  const handleFileChange = (e: React.ChangeEvent<HTMLInputElement>) => {
+    const files = Array.from(e.target.files || []);
+    props.onChange?.(files);
+  };
+
+  return (
+    <div>
+      <Button
+        variant={props.variant}
+        onClick={() => fileInputRef.current?.click()}
+        className={props.className}
+      >
+        {props.children}
+      </Button>
+      <input
+        ref={fileInputRef}
+        type="file"
+        multiple={props.multiple}
+        accept="image/*"
+        onChange={handleFileChange}
+        className="hidden"
+        aria-label="Upload image"
+      />
+    </div>
+  );
+}

apps/dashboard/src/app/nebula-app/(app)/api/types.ts

@@ -8,6 +8,10 @@ type NebulaUserMessageContentItem =
       type: "image";
       image_url: string;
     }
+  | {
+      type: "image";
+      b64: string;
+    }
   | {
       type: "text";
       text: string;