feat: Implement core application structure, AI extraction, persistence, and Telegram bot modules with updated configuration and dependencies.

app/preprocessing/language_detect.py

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+"""
+Language detection functions.
+"""
+
+def detect_language(text: str) -> str:
+    """
+    Detects the language of a given text.
+    Stub function.
+    """
+    # In a real app, use a library like 'langdetect' or 'google-cloud-translate'
+    return "en" # Assume English for now

app/preprocessing/normalize_text.py

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+"""
+Text normalization functions.
+"""
+
+def normalize_text(text: str) -> str:
+    """
+    Normalizes a string by converting it to lowercase and stripping whitespace.
+    """
+    if not text:
+        return ""
+    return text.lower().strip()

app/preprocessing/validators.py

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+"""
+Data validation functions.
+"""
+
+def is_valid_expense(data: dict) -> bool:
+    """
+    Validates if the extracted data for an expense is plausible.
+    Stub function.
+    """
+    # Example validation: amount must be positive
+    if "amount" in data and data["amount"] <= 0:
+        return False
+    return True