feat: CSV import and batch reconciliation UI

- Add reconciled_with_id column to transactions (links manual → statement tx)
- CSV import wizard: 4-step modal (upload → map columns → review → done)
  - Handles any bank format via column mapping with localStorage presets
  - Single signed or separate debit/credit column modes
  - Editable preview table before committing
  - Auto-tags all imported rows with 'csv-import'
- Batch reconcile page: shows all unreconciled manual transactions with
  potential statement matches (date ±3 days, amount ±1%) pre-fetched
  - Select matches across multiple rows, apply all at once
  - Copies overrides/tags/splits from manual → statement tx atomically
  - Manual tx marked reconciled (linked), hidden from main transactions view
  - Transactions with no matches shown separately
- Import CSV button on transactions page
- Reconcile nav item in sidebar

src/components/sidebar.tsx

@@ -13,6 +13,7 @@ const NAV_ITEMS = [
   { href: "/merchants", label: "Merchants", icon: "store" },
   { href: "/tags", label: "Tags", icon: "tag" },
   { href: "/rules", label: "Rules", icon: "settings" },
+  { href: "/reconcile", label: "Reconcile", icon: "git-merge" },
 ];
 
 const ICONS: Record<string, React.ReactNode> = {
@@ -52,6 +53,11 @@ const ICONS: Record<string, React.ReactNode> = {
       <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M9.663 17h4.673M12 3v1m6.364 1.636l-.707.707M21 12h-1M4 12H3m1.343-5.657l-.707-.707m2.828 9.9a5 5 0 117.072 0l-.548.547A3.374 3.374 0 0014 18.469V19a2 2 0 11-4 0v-.531c0-.895-.356-1.754-.988-2.386l-.548-.547z" />
     </svg>
   ),
+  "git-merge": (
+    <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+      <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M6 3v12M18 9a3 3 0 100-6 3 3 0 000 6zm0 0v12M6 15a3 3 0 100 6 3 3 0 000-6zm0 0c0-4 3-6 6-6h6" />
+    </svg>
+  ),
   store: (
     <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
       <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M3 3h2l.4 2M7 13h10l4-8H5.4M7 13L5.4 5M7 13l-2.293 2.293c-.63.63-.184 1.707.707 1.707H17m0 0a2 2 0 100 4 2 2 0 000-4zm-8 2a2 2 0 11-4 0 2 2 0 014 0z" />