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/file_validation.py

@@ -0,0 +1,91 @@
+# bot/modules/file_validation.py
+# This module provides functions for validating files before processing.
+
+import logging
+from telegram import Document
+
+# Set up logging
+logger = logging.getLogger(__name__)
+
+# --- Configuration ---
+# Whitelist of allowed MIME types. Prevents processing of potentially harmful files.
+# Examples: 'application/pdf', 'image/jpeg', 'application/msword',
+# 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'
+ALLOWED_MIME_TYPES = {
+    'application/pdf',
+    'application/msword',
+    'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
+    'text/plain',
+    'image/jpeg',
+    'image/png'
+}
+
+# Maximum file size in bytes (e.g., 10 * 1024 * 1024 for 10 MB)
+MAX_FILE_SIZE_BYTES = 10 * 1024 * 1024  # 10 MB
+
+# --- Validation Functions ---
+
+def is_file_type_allowed(document: Document) -> bool:
+    """
+    Checks if the document's MIME type is in the allowed whitelist.
+
+    Args:
+        document: The Telegram Document object to check.
+
+    Returns:
+        True if the MIME type is allowed, False otherwise.
+    """
+    if not document or not document.mime_type:
+        logger.warning("Document or its MIME type is missing.")
+        return False
+
+    logger.info(f"Validating file type: {document.mime_type}")
+
+    if document.mime_type in ALLOWED_MIME_TYPES:
+        logger.info("File type is allowed.")
+        return True
+    else:
+        logger.warning(f"File type '{document.mime_type}' is not in the allowed list.")
+        return False
+
+def is_file_size_acceptable(document: Document) -> bool:
+    """
+    Checks if the document's file size is within the acceptable limit.
+
+    Args:
+        document: The Telegram Document object to check.
+
+    Returns:
+        True if the file size is acceptable, False otherwise.
+    """
+    if not document or document.file_size is None:
+        logger.warning("Document or its file size is missing.")
+        return False
+
+    logger.info(f"Validating file size: {document.file_size} bytes.")
+
+    if document.file_size <= MAX_FILE_SIZE_BYTES:
+        logger.info("File size is acceptable.")
+        return True
+    else:
+        logger.warning(f"File size {document.file_size} exceeds the limit of {MAX_FILE_SIZE_BYTES} bytes.")
+        return False
+
+def validate_document(document: Document) -> (bool, str):
+    """
+    Performs all validation checks on a document.
+
+    Args:
+        document: The Telegram Document object to validate.
+
+    Returns:
+        A tuple containing a boolean indicating if the document is valid,
+        and a string message explaining the result.
+    """
+    if not is_file_type_allowed(document):
+        return False, f"Unsupported file type: {document.mime_type}. Please upload a supported document."
+
+    if not is_file_size_acceptable(document):
+        return False, f"File is too large. The maximum allowed size is {MAX_FILE_SIZE_BYTES // 1024 // 1024} MB."
+
+    return True, "File is valid and can be processed."