refactor: Streamline EPUB handling with new split modes and improved error management

- Removed legacy AI Tool references and unnecessary fields from the README and various components.
- Introduced new EPUB split modes (toc, regex, tag) to enhance flexibility in chapter extraction.
- Updated import and chapter management components to utilize the new EPUB split functionality.
- Improved error handling in the login API route for better user feedback.
- Cleaned up unused files and optimized the overall code structure for maintainability.

lib/epub-split.ts

@@ -0,0 +1,31 @@
+export type EpubSplitMode = "toc" | "regex" | "tag"
+
+export const EPUB_HTML_TAG_PRESETS = [
+  { id: "a", name: "Thẻ <a> (anchor / mục lục liên kết)", tag: "a" },
+  { id: "h2", name: "Thẻ <h2>", tag: "h2" },
+  { id: "h1", name: "Thẻ <h1>", tag: "h1" },
+  { id: "h3", name: "Thẻ <h3>", tag: "h3" },
+  { id: "p", name: "Thẻ <p>", tag: "p" },
+] as const
+
+export const DEFAULT_EPUB_CHAPTER_TAG = "a"
+
+export function splitModeLabel(mode: string | undefined): string {
+  if (mode === "regex") return "Regex"
+  if (mode === "tag") return "Thẻ HTML"
+  return "TOC"
+}
+
+export function appendEpubSplitFormFields(
+  form: FormData,
+  splitMode: EpubSplitMode,
+  options?: { chapterRegex?: string; chapterTag?: string },
+) {
+  form.append("splitMode", splitMode)
+  if (splitMode === "regex" && options?.chapterRegex) {
+    form.append("chapterRegex", options.chapterRegex)
+  }
+  if (splitMode === "tag") {
+    form.append("chapterTag", (options?.chapterTag || DEFAULT_EPUB_CHAPTER_TAG).trim() || DEFAULT_EPUB_CHAPTER_TAG)
+  }
+}