Add persistent payee duplicate ignores and expose them in Settings

[Copilot]

This updates payee duplicate handling so suggested pairs can be marked as not duplicates and excluded from future detection runs. It also adds a settings surface for reviewing and removing ignored pairs, and includes that data in settings import/export.

• Payee duplicate workflow

  • Adds a Not a Duplicate action to suggested payee duplicates.
  • Persists ignored payee pairs in normalized form so A/B and B/A are treated as the same pair.
  • Filters ignored pairs out of subsequent duplicate detection results.

• Settings UI

  • Adds an Ignored Duplicates settings section/tab.
  • Reuses the existing searchable table pattern for browsing ignored pairs.
  • Supports deleting ignored pairs to re-enable future suggestions.

• Settings import/export

  • Extends settings serialization to include ignored payee duplicate pairs.
  • Keeps import backward-compatible by treating the new field as optional.

• Data model / plumbing

  • Introduces a small settings-backed store for ignored payee duplicate pairs.
  • Normalizes pairs on decode/storage to avoid duplicate entries and inconsistent ordering.

let ignoredPair = IgnoredPayeeDuplicatePair(payee1: duplicate.payee1, payee2: duplicate.payee2)
IgnoredPayeeDuplicateSettings.add(ignoredPair)

guard !ignoredPairs.contains(IgnoredPayeeDuplicatePair(payee1: payee1, payee2: payee2)) else {
    continue
}