Make the formula bar mouse-resizable and wrapping

Switches the formula bar from a single-line <input> to a <textarea>:

- A plain <textarea> gets a free, native mouse-draggable resize handle in
  its bottom-right corner (CSS resize: vertical) -- exactly the "erweiterbar/
  erhöhbar mit der Maus" ask, no custom drag code needed.
- Unlike the old <input>, it actually wraps a long formula instead of just
  scrolling it sideways, so dragging the handle taller has something to
  show (min-height keeps the collapsed case looking like before; max-height
  caps it at half the viewport).
- Brought its keyboard handling in line with the in-cell editor from the
  last two changes: Alt+Enter/Cmd+Enter insert a literal newline, F4 cycles
  every reference a selection overlaps, Escape reverts and blurs.
- .formula-bar switches to align-items: flex-start (with matching top
  margins on the labels) so the cell-name/fx labels stay pinned to the
  first line instead of vertically centering in a now-tall box.

Verified interactively: dragging the handle down 80px grows the bar from
~34px to ~113px; Alt+Enter inserts a real newline in the (now multi-line-
capable) field.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -112,6 +112,12 @@ Ein Zeilenumbruch bleibt auch nach dem Committen erhalten und wird in der
 Zelle als solcher dargestellt (umbrechend statt einzeiliger Ellipse), auf die
 Zeilenhöhe der Tabelle geklemmt.
 
+**Formelleiste** (`fx`, oben): ein `<textarea>` statt eines einzeiligen Felds
+— dadurch **umbricht** eine lange Formel statt seitwärts wegzuscrollen, und
+an der unteren Kante lässt sie sich per **Maus** (natives `resize: vertical`)
+auf beliebig viele Zeilen aufziehen, um mehr auf einmal zu sehen. `Alt`+`Enter`
+bzw. `Cmd`+`Enter`, `F4` und `Esc` verhalten sich wie im In-Zellen-Editor.
+
 ### Zell-Formatierung
 
 Auswahl (Zelle, Bereich, Mehrfachauswahl, ganze Zeile/Spalte über den Kopf) → im

src/components/FormulaBar.vue

@@ -35,8 +35,7 @@ function onEscape() {
 /** F4: cycle relative -> absolute -> row-locked -> col-locked (Excel/Numbers
  *  "Bezug sperren") -- for the reference at the caret, or every reference a
  *  real text selection overlaps at once. */
-function onF4(e: KeyboardEvent) {
-  const el = e.target as HTMLInputElement;
+function onF4(el: HTMLTextAreaElement) {
   const start = el.selectionStart ?? draft.value.length;
   const end = el.selectionEnd ?? start;
   const res = cycleReferenceLocks(draft.value, start, end);
@@ -44,6 +43,31 @@ function onF4(e: KeyboardEvent) {
   draft.value = res.text;
   nextTick(() => el.setSelectionRange(res.start, res.end));
 }
+function onKeydown(e: KeyboardEvent) {
+  const el = e.target as HTMLTextAreaElement;
+  // Alt+Enter (Windows/Excel-365-Mac) or Cmd+Enter (a macOS-safe fallback --
+  // Option is a compose key there, so `altKey` alone isn't fully reliable;
+  // `e.code` sidesteps `key` being altered by that composition).
+  const isEnter = e.key === 'Enter' || e.code === 'Enter' || e.code === 'NumpadEnter';
+  if (isEnter && (e.altKey || e.metaKey)) {
+    e.preventDefault();
+    const start = el.selectionStart ?? draft.value.length;
+    const end = el.selectionEnd ?? start;
+    draft.value = draft.value.slice(0, start) + '\n' + draft.value.slice(end);
+    nextTick(() => el.setSelectionRange(start + 1, start + 1));
+    return;
+  }
+  if (isEnter) {
+    e.preventDefault();
+    onEnter();
+  } else if (e.key === 'Escape') {
+    e.preventDefault();
+    onEscape();
+  } else if (e.key === 'F4') {
+    e.preventDefault();
+    onF4(el);
+  }
+}
 </script>
 
 <template>
@@ -52,17 +76,16 @@ function onF4(e: KeyboardEvent) {
       {{ store.activeCellName.value }}
     </span>
     <span class="fx">fx</span>
-    <input
+    <textarea
       v-model="draft"
       class="formula-input"
-      type="text"
       spellcheck="false"
+      rows="1"
       placeholder="Wert oder =Formel"
+      title="Ziehen an der unteren Kante, um mehr Zeilen zu zeigen"
       @focus="focused = true"
       @blur="onBlur"
-      @keydown.enter.prevent="onEnter"
-      @keydown.esc.prevent="onEscape"
-      @keydown.f4.prevent="onF4"
+      @keydown="onKeydown"
     />
   </div>
 </template>
@@ -70,7 +93,7 @@ function onF4(e: KeyboardEvent) {
 <style scoped>
 .formula-bar {
   display: flex;
-  align-items: center;
+  align-items: flex-start;
   gap: 10px;
   padding: 6px 12px;
   background: var(--surface);
@@ -79,6 +102,7 @@ function onF4(e: KeyboardEvent) {
 .cell-name {
   min-width: 128px;
   max-width: 128px;
+  margin-top: 6px;
   font-weight: 600;
   font-size: 12px;
   color: var(--text-dim);
@@ -97,12 +121,19 @@ function onF4(e: KeyboardEvent) {
   }
 }
 .fx {
+  margin-top: 6px;
   font-style: italic;
   color: var(--text-dim);
   font-size: 13px;
 }
+/* a plain <textarea> gives a free, native mouse-draggable resize handle
+   (bottom-right corner) -- exactly the "erweiterbar/erhöhbar mit der Maus"
+   ask -- and, unlike the old <input>, actually wraps a long formula instead
+   of just scrolling it sideways, so growing the box has something to show. */
 .formula-input {
   flex: 1;
+  min-height: 30px;
+  max-height: 50vh;
   border: 1px solid var(--border);
   border-radius: var(--radius-sm);
   padding: 6px 10px;
@@ -110,6 +141,10 @@ function onF4(e: KeyboardEvent) {
   font-variant-numeric: tabular-nums;
   color: var(--text);
   background: var(--surface-2);
+  resize: vertical;
+  overflow-y: auto;
+  white-space: pre-wrap;
+  word-break: break-word;
 }
 .formula-input:focus {
   outline: none;