Auto-sizing cell editor, multi-ref F4, and Alt+Enter line breaks

1. In-cell editor width/height ("nur in der Breite der Zelle angezeigt"):
   the editor now lives as an overlay (like the clip/fill markers) instead
   of inside its <td>, so it can grow past the cell -- width first, up to
   an approximated display-width cap, then wrapping and growing height.
   Sized via a hidden mirror element (same font/padding, real DOM
   measurement -- a <textarea> can't self-size to content with CSS alone).

2. F4 now cycles every reference a real text selection overlaps, each from
   its own lock state, not just the one at the caret -- select a stretch of
   formula spanning several references and F4 adjusts all of them at once,
   same as Excel. cycleReferenceLock(formula, caret) -> cycleReferenceLocks
   (formula, start, end); a collapsed selection (start === end) keeps the
   old single-reference caret behaviour. Wired into both the in-cell editor
   and the formula bar.

3. Alt+Enter inserts a literal newline in the editor instead of committing
   (explicit splice at the caret, not relying on the textarea's native
   Enter handling, which isn't consistently reachable for Alt+Enter). A
   cell holding a newline displays it wrapped (.cell.multiline) instead of
   collapsing to one ellipsised line.

Along the way: a <td>'s own max-height doesn't cap table-row growth in any
browser (a table-layout quirk) -- a wrapped multi-line cell was silently
growing its row past rowH(r), which would have desynced every pixel
position computed from rowH()/rowTop() (the overlays, sticky frozen panes,
the row-resize handle). Fixed by moving cell text into its own block-level
.cell-content child, which *does* respect max-height + overflow:hidden.

Verified interactively against the dev server with Playwright: a long
formula gets a ~300px editor instead of the 104px cell; Alt+Enter produces
a real "\n" that survives commit and displays wrapped, with the row height
unchanged (26px, not the ~40px it grew to before the .cell-content fix);
F4 on a full-formula selection turns every reference absolute in one press
and keeps cycling all of them on repeated presses; existing selection,
copy/paste and fill-handle behaviour all regression-checked clean.

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

src/components/FormulaBar.vue

@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { nextTick, ref, watch } from 'vue';
 import { useDocument } from '../store/document';
-import { cycleReferenceLock } from '../engine';
+import { cycleReferenceLocks } from '../engine';
 
 const store = useDocument();
 const draft = ref('');
@@ -32,14 +32,17 @@ function onEscape() {
   draft.value = store.activeCellInput.value;
   (document.activeElement as HTMLElement)?.blur();
 }
-/** F4: cycle relative -> absolute -> row-locked -> col-locked for the cell
- *  reference at the caret (Excel/Numbers "Bezug sperren"). */
+/** 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;
-  const res = cycleReferenceLock(draft.value, el.selectionStart ?? draft.value.length);
+  const start = el.selectionStart ?? draft.value.length;
+  const end = el.selectionEnd ?? start;
+  const res = cycleReferenceLocks(draft.value, start, end);
   if (!res) return;
   draft.value = res.text;
-  nextTick(() => el.setSelectionRange(res.caret, res.caret));
+  nextTick(() => el.setSelectionRange(res.start, res.end));
 }
 </script>