Fix decimal parsing bug + contribution and pre-fill features

BUG FIX: parseDecimal ignored locale mismatch between currency and device.
CurrencyFormatter.locale(for: "EUR") could return any EUR locale (e.g.
en_IE with decimal='.'), causing "408857,62" to be parsed as 40,885,762.
New CurrencyFormatter.parseUserInput() uses digit-position detection:
a separator followed by ≤2 digits at the end is decimal, otherwise
it is a thousands separator. Fully locale-independent.

FEATURE: Contribution field now always visible in AddSnapshotView.
Previously gated behind inputMode == .detailed; now a toggle available
regardless of account mode.

FEATURE: BatchUpdateView pre-fills each text field with the source's
current value so the user only edits what changed. Adds an optional
contribution field per source row, persisted on save.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

PortfolioJournal/ViewModels/SnapshotFormViewModel.swift

@@ -1,5 +1,6 @@
 import Foundation
 import Combine
+import UIKit
 
 @MainActor
 class SnapshotFormViewModel: ObservableObject {
@@ -16,6 +17,8 @@ class SnapshotFormViewModel: ObservableObject {
 
     @Published var isValid = false
     @Published var errorMessage: String?
+    @Published var clipboardValue: String?
+    private var rawClipboardString: String?
 
     // MARK: - Mode
 
@@ -102,53 +105,11 @@ class SnapshotFormViewModel: ObservableObject {
     // MARK: - Parsing
 
     private func parseDecimal(_ string: String) -> Decimal? {
-        let locale = CurrencyFormatter.locale(for: currencyCode)
-        let cleaned = string
-            .replacingOccurrences(of: currencySymbol, with: "")
-            .replacingOccurrences(of: locale.groupingSeparator ?? "", with: "")
-            .trimmingCharacters(in: .whitespaces)
-
-        guard !cleaned.isEmpty else { return nil }
-
-        let decimalSeparator = locale.decimalSeparator ?? "."
-        let usesAlternateDecimal =
-            (decimalSeparator == "," && cleaned.contains(".") && !cleaned.contains(",")) ||
-            (decimalSeparator == "." && cleaned.contains(",") && !cleaned.contains("."))
-
-        if usesAlternateDecimal {
-            let normalized = cleaned
-                .replacingOccurrences(of: ",", with: ".")
-            let formatter = NumberFormatter()
-            formatter.numberStyle = .decimal
-            formatter.locale = Locale(identifier: "en_US_POSIX")
-            return formatter.number(from: normalized)?.decimalValue
-        }
-
-        let formatter = NumberFormatter()
-        formatter.numberStyle = .decimal
-        formatter.locale = locale
-
-        if let result = formatter.number(from: cleaned)?.decimalValue {
-            return result
-        }
-
-        // Fallback for mixed locale input
-        let normalized = cleaned
-            .replacingOccurrences(of: locale.decimalSeparator ?? ",", with: ".")
-            .replacingOccurrences(of: ",", with: ".")
-        formatter.locale = Locale(identifier: "en_US_POSIX")
-        return formatter.number(from: normalized)?.decimalValue
+        CurrencyFormatter.parseUserInput(string, currencySymbol: currencySymbol)
     }
 
     private func formatDecimalForInput(_ decimal: Decimal) -> String {
-        let locale = CurrencyFormatter.locale(for: currencyCode)
-        let formatter = NumberFormatter()
-        formatter.numberStyle = .decimal
-        formatter.locale = locale
-        formatter.minimumFractionDigits = 2
-        formatter.maximumFractionDigits = 2
-        formatter.groupingSeparator = ""
-        return formatter.string(from: decimal as NSDecimalNumber) ?? ""
+        CurrencyFormatter.formatForInput(decimal, currencyCode: currencyCode)
     }
 
     // MARK: - Computed Properties
@@ -236,6 +197,41 @@ class SnapshotFormViewModel: ObservableObject {
         date = Date()
     }
 
+    // MARK: - Clipboard
+
+    func checkClipboard() {
+        guard let raw = UIPasteboard.general.string else {
+            clipboardValue = nil
+            rawClipboardString = nil
+            return
+        }
+
+        guard let parsed = parseDecimal(raw), parsed > 0 else {
+            clipboardValue = nil
+            rawClipboardString = nil
+            return
+        }
+
+        // Don't suggest if it matches what's already typed
+        let formatted = formatDecimalForInput(parsed)
+        if formatted == valueString {
+            clipboardValue = nil
+            rawClipboardString = nil
+            return
+        }
+
+        rawClipboardString = raw
+        clipboardValue = CurrencyFormatter.format(parsed, style: .currency, maximumFractionDigits: 2)
+    }
+
+    func applyClipboardValue() {
+        guard let raw = rawClipboardString,
+              let parsed = parseDecimal(raw) else { return }
+        valueString = formatDecimalForInput(parsed)
+        clipboardValue = nil
+        rawClipboardString = nil
+    }
+
     // MARK: - Date Validation
 
     var isDateInFuture: Bool {