Refactor and enhance type hints across multiple modules

- Updated the `from_tuple` method in `Prof` class to specify return type.
- Added type hints for various methods in `LehmannsClient`, `OpenAI`, `WebRequest`, and `ZoteroController` classes to improve code clarity and type safety.
- Modified `pdf_to_csv` function to return a string instead of a DataFrame.
- Enhanced error handling and type hints in `wordparser` and `xmlparser` modules.
- Removed unused UI file `Ui_medianadder.ts`.
- Improved the layout and structure of the `semesterapparat_ui` to enhance user experience.
- Updated file picker to support `.doc` files in addition to `.docx`.
- Added unique item handling in `Ui` class to prevent duplicates in apparat list.
- General code cleanup and consistency improvements across various files.

src/backend/catalogue.py

@@ -1,3 +1,5 @@
+from typing import List
+
 import regex
 import requests
 from bs4 import BeautifulSoup
@@ -33,13 +35,13 @@ class Catalogue:
         response = requests.get(link, timeout=self.timeout)
         return response.text
 
-    def get_book_links(self, searchterm: str):
+    def get_book_links(self, searchterm: str) -> List[str]:
         response = self.search_book(searchterm)
         soup = BeautifulSoup(response, "html.parser")
         links = soup.find_all("a", class_="title getFull")
-        res = []
+        res: List[str] = []
         for link in links:
-            res.append(BASE + link["href"])
+            res.append(BASE + link["href"])  # type: ignore
         return res
 
     def get_book(self, searchterm: str):