feat: Parser-Basis, Bank-Erkennung, Saldo-/Duplikat-Pruefung

- ParsedTransaction und ParsedStatement Datenklassen
- parse_german_amount(): German format number parsing (1.234,56 -> Decimal)
- parse_german_date(): DD.MM.YYYY date parsing with optional year
- detect_bank(): Recognize VR/HVB/DKB from text markers
- balance_difference(): Validate statement balance consistency
- dedup_hash(): SHA256-based transaction deduplication

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

finance/app/parsers/detect.py

@@ -0,0 +1,12 @@
+MARKERS = [
+    ("vr", ["Volksbank", "Raiffeisenbank", "VR-Bank", "VR Bank"]),
+    ("hvb", ["HypoVereinsbank", "UniCredit"]),
+    ("dkb", ["Deutsche Kreditbank", "DKB"]),
+]
+
+
+def detect_bank(text: str) -> str | None:
+    for bank, needles in MARKERS:
+        if any(n in text for n in needles):
+            return bank
+    return None