feat: Phase 4 – CSV-Import (Templates, Prüfansicht, Duplikat/Transfer-Erkennung, Undo)

Backend:
- Modelle + Migration 0005: import_templates, import_batches, categorization_rules;
  transactions um import_batch_id + import_hash erweitert.
- services/csv_import: Datei parsen (Trennzeichen, Dezimal-/Datumsformat, Kodierung,
  Header/Skip, Vorzeichen vs. Soll/Haben), Vorschau mit Duplikat-Erkennung (Hash),
  interner-Transfer-Erkennung via IBAN, lernender Auto-Kategorisierung; Buchen mit
  Batch und Undo.
- routers/imports: Templates (CRUD), Roh-Vorschau, Prüf-Vorschau, Buchen, Verlauf,
  Rückgängig. pytest: Parsing, Duplikate, Transfer, Buchen, Undo, Lernen.

Frontend:
- Import-Seite: Konto+Datei, Format/Spaltenzuordnung (mit Roh-Vorschau),
  editierbare Prüfansicht (Kategorie/Typ/Zielkonto, Duplikate markiert),
  Buchen, Import-Verlauf mit Undo; Vorlagen speichern; i18n DE/EN.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/locales/en.json

@@ -195,5 +195,52 @@
     "incomeLabel": "Label",
     "incomeCategory": "Category",
     "targetAccount": "Target account"
+  },
+  "import": {
+    "title": "CSV import",
+    "step1": "1 · Account & file",
+    "step2": "2 · Format",
+    "step3": "3 · Map columns",
+    "step4": "4 · Review & import",
+    "account": "Target account",
+    "file": "CSV file",
+    "template": "Template",
+    "templateManual": "Configure manually",
+    "delimiter": "Delimiter",
+    "decimal": "Decimal separator",
+    "dateFormat": "Date format",
+    "encoding": "Encoding",
+    "amountMode": "Amount columns",
+    "skipRows": "Skip rows",
+    "hasHeader": "First row is a header",
+    "modeSigned": "Single amount (signed)",
+    "modeDebitCredit": "Separate debit/credit columns",
+    "modeAbsExpense": "Single amount (always expense)",
+    "readFile": "Read file",
+    "makePreview": "Build preview",
+    "saveTemplate": "Save as template",
+    "templateName": "Template name",
+    "colDate": "Date",
+    "colAmount": "Amount",
+    "colDebit": "Debit (out)",
+    "colCredit": "Credit (in)",
+    "colPayee": "Payee",
+    "colPurpose": "Purpose",
+    "colIban": "Counterparty IBAN",
+    "makePreviewHint": "Map at least date and amount.",
+    "commit": "Import {{n}} transactions",
+    "imported": "Imported {{n}} transactions.",
+    "importedCount": "{{n}} imported",
+    "typeCol": "Type",
+    "payeeCol": "Payee / purpose",
+    "badDate": "Date?",
+    "duplicate": "Duplicate",
+    "chooseAccount": "Choose account",
+    "history": "Import history",
+    "undo": "Undo",
+    "undoConfirm": "Remove all transactions from {{file}}?",
+    "undone": "undone",
+    "needFile": "Please choose a CSV file first.",
+    "needFileAccount": "Please choose an account and a file."
   }
 }