feat(ui): add fast entry for many purchases at once

A grocery trip is twenty lines, and opening the full dialog twenty times
is the thing this exists to avoid.

PurchaseDialog gains a One / Many toggle, shown only when adding — editing
an existing purchase edits exactly one, so the toggle is hidden there. In
Many mode the date, post and currency are set once at the top and each line
is just a description and an amount; Enter on an amount starts the next
line, so a receipt can be typed without leaving the keyboard. Blank trailing
rows are ignored rather than flagged.

The whole batch commits in a single mutate: one write, one queue entry, and
no way to half-commit a shopping trip.

Lines are deliberately simple. A line needing a split or a payment plan is
saved plain and then edited from the month view — building per-line split
and plan editors would have been most of the work for a case the grocery
run never hits, and would have slowed the common path.

Line logic lives in a pure module (src/ui/bulkEntry.ts) following the
purchaseForm.ts pattern, so it is testable with no DOM: 20 tests covering
blank-row handling, per-row validation messages, the running total, and
that N lines become N purchases landing wholly in the shared post. Each
line is built through the same toPurchase the single form uses, so there
is one definition of what a purchase is.

Validation mirrors validatePurchase in what it deliberately does NOT
reject: a negative amount is a refund, not an error.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/ui/components/BulkLines.tsx

@@ -0,0 +1,118 @@
+import { useRef } from "react";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import { formatMoney } from "../format.ts";
+import { bulkTotal, isBlankLine, type BulkDraft } from "../bulkEntry.ts";
+
+interface Props {
+  draft: BulkDraft;
+  onChange: (next: BulkDraft) => void;
+}
+
+/**
+ * The row list for fast entry. Two fields per line is the whole point — Enter
+ * in the amount field commits the row and focuses a fresh one, so a grocery
+ * receipt can be typed without ever leaving the keyboard.
+ */
+export function BulkLines({ draft, onChange }: Props) {
+  const amountRefs = useRef<Array<HTMLInputElement | null>>([]);
+
+  function updateLine(index: number, changes: Partial<BulkDraft["lines"][number]>) {
+    onChange({
+      ...draft,
+      lines: draft.lines.map((line, i) => (i === index ? { ...line, ...changes } : line)),
+    });
+  }
+
+  function addLine(focusIndex?: number) {
+    onChange({ ...draft, lines: [...draft.lines, { description: "", amount: 0 }] });
+    if (focusIndex !== undefined) {
+      // Focus after React has rendered the new row.
+      requestAnimationFrame(() => amountRefs.current[focusIndex]?.focus());
+    }
+  }
+
+  function removeLine(index: number) {
+    const lines = draft.lines.filter((_, i) => i !== index);
+    onChange({ ...draft, lines: lines.length > 0 ? lines : [{ description: "", amount: 0 }] });
+  }
+
+  const filledCount = draft.lines.filter((line) => !isBlankLine(line)).length;
+
+  return (
+    <fieldset className="space-y-2">
+      <div className="flex items-center justify-between">
+        <Label>Lines</Label>
+        <span className="text-xs text-muted-foreground">
+          Enter on an amount starts the next line
+        </span>
+      </div>
+
+      <div className="max-h-72 space-y-1 overflow-y-auto pr-1">
+        {draft.lines.map((line, index) => (
+          <div key={index} className="flex items-center gap-2">
+            <span className="w-5 shrink-0 text-right text-xs text-muted-foreground">
+              {index + 1}
+            </span>
+            <Input
+              className="h-8 flex-1"
+              placeholder="What was it?"
+              value={line.description}
+              onChange={(event) => {
+                const description = event.target.value;
+                updateLine(index, { description });
+              }}
+              onKeyDown={(event) => {
+                if (event.key === "Enter") {
+                  event.preventDefault();
+                  amountRefs.current[index]?.focus();
+                }
+              }}
+            />
+            <Input
+              ref={(el) => {
+                amountRefs.current[index] = el;
+              }}
+              className="font-money h-8 w-28"
+              type="number"
+              step="0.01"
+              placeholder="0.00"
+              value={line.amount === 0 ? "" : line.amount}
+              onChange={(event) => {
+                const amount = Number(event.target.value) || 0;
+                updateLine(index, { amount });
+              }}
+              onKeyDown={(event) => {
+                if (event.key === "Enter") {
+                  event.preventDefault();
+                  if (index === draft.lines.length - 1) addLine(index + 1);
+                  else amountRefs.current[index + 1]?.focus();
+                }
+              }}
+            />
+            <Button
+              type="button"
+              size="sm"
+              variant="ghost"
+              aria-label={`Remove line ${index + 1}`}
+              onClick={() => removeLine(index)}
+            >
+              remove
+            </Button>
+          </div>
+        ))}
+      </div>
+
+      <div className="flex items-center justify-between text-xs">
+        <Button type="button" size="sm" variant="outline" onClick={() => addLine(draft.lines.length)}>
+          Add line
+        </Button>
+        <span className="text-muted-foreground">
+          {filledCount} line{filledCount === 1 ? "" : "s"} &middot;{" "}
+          <span className="font-money">{formatMoney(bulkTotal(draft), draft.currency)}</span>
+        </span>
+      </div>
+    </fieldset>
+  );
+}