feat: Complete sprint tasks

- Add file upload security validation to prevent processing of potentially harmful files.
- Update python-telegram-bot to a pinned version and upgrade other dependencies.
- Implement Whisper transcription agent for voice message processing.
- Restore Google Calendar functionality with provided credentials.

bot/modules/transcription.py

@@ -0,0 +1,47 @@
+# bot/modules/transcription.py
+# This module handles audio transcription using the Whisper API.
+
+import logging
+import os
+from openai import OpenAI
+from bot.config import OPENAI_API_KEY
+
+# Set up logging
+logger = logging.getLogger(__name__)
+
+# Initialize the OpenAI client
+if not OPENAI_API_KEY:
+    logger.error("OPENAI_API_KEY is not configured in environment variables.")
+    client = None
+else:
+    client = OpenAI(api_key=OPENAI_API_KEY)
+
+def transcribe_audio(file_path: str) -> str:
+    """
+    Transcribes an audio file using the Whisper API.
+
+    Args:
+        file_path: The path to the audio file to transcribe.
+
+    Returns:
+        The transcribed text, or an error message if transcription fails.
+    """
+    if not client:
+        return "Error: OpenAI API key is not configured."
+
+    if not os.path.exists(file_path):
+        logger.error(f"Audio file not found at: {file_path}")
+        return "Error: Audio file not found."
+
+    try:
+        logger.info(f"Transcribing audio from: {file_path}")
+        with open(file_path, "rb") as audio_file:
+            transcript = client.audio.transcriptions.create(
+                model="whisper-1",
+                file=audio_file
+            )
+        logger.info("Transcription successful.")
+        return transcript.text
+    except Exception as e:
+        logger.error(f"Error during audio transcription: {e}")
+        return "Error: Could not transcribe audio."