feat: add PDF and text file upload support (#205)

- Add client-side PDF text extraction using unpdf library
- Support text files (.txt, .md, .json, .csv, .py, .js, .ts, etc.)
- Add file preview with character count for PDF/text files
- Add 150k character limit for extracted content
- Highlight Paper to Diagram example with NEW badge
- Fix React hydration error by adding explicit IDs to ResizablePanelGroup
- Remove code duplication by centralizing file utilities in pdf-utils.ts

lib/pdf-utils.ts

@@ -0,0 +1,72 @@
+import { extractText, getDocumentProxy } from "unpdf"
+
+// Maximum characters allowed for extracted text
+export const MAX_EXTRACTED_CHARS = 150000 // 150k chars
+
+// Text file extensions we support
+const TEXT_EXTENSIONS = [
+    ".txt",
+    ".md",
+    ".markdown",
+    ".json",
+    ".csv",
+    ".xml",
+    ".html",
+    ".css",
+    ".js",
+    ".ts",
+    ".jsx",
+    ".tsx",
+    ".py",
+    ".java",
+    ".c",
+    ".cpp",
+    ".h",
+    ".go",
+    ".rs",
+    ".yaml",
+    ".yml",
+    ".toml",
+    ".ini",
+    ".log",
+    ".sh",
+    ".bash",
+    ".zsh",
+]
+
+/**
+ * Extract text content from a PDF file
+ * Uses unpdf library for client-side extraction
+ */
+export async function extractPdfText(file: File): Promise<string> {
+    const buffer = await file.arrayBuffer()
+    const pdf = await getDocumentProxy(new Uint8Array(buffer))
+    const { text } = await extractText(pdf, { mergePages: true })
+    return text as string
+}
+
+/**
+ * Check if a file is a PDF
+ */
+export function isPdfFile(file: File): boolean {
+    return file.type === "application/pdf" || file.name.endsWith(".pdf")
+}
+
+/**
+ * Check if a file is a text file
+ */
+export function isTextFile(file: File): boolean {
+    const name = file.name.toLowerCase()
+    return (
+        file.type.startsWith("text/") ||
+        file.type === "application/json" ||
+        TEXT_EXTENSIONS.some((ext) => name.endsWith(ext))
+    )
+}
+
+/**
+ * Extract text content from a text file
+ */
+export async function extractTextFileContent(file: File): Promise<string> {
+    return await file.text()
+}