Add a sheet qualifier: "Blatt!Tabelle::Zelle", table names unique per sheet

Table names were document-unique; now they're unique per sheet only --
two different sheets may each hold a table called "Umsatz". A plain,
unqualified reference (Umsatz!B2 / Umsatz::B2, unchanged from before)
resolves to the table on the SAME sheet as the formula referencing it
when the name is otherwise ambiguous, falling back to the single
document-wide match when it isn't ambiguous at all -- exactly as
before for every existing formula. The new explicit 3-part form
(Analyse!Umsatz::B2, quoted where a name has spaces) always targets
the named sheet's table regardless of where the formula itself lives,
for the case that's still genuinely ambiguous.

Engine: parser.ts's afterFirstQualifierToken() disambiguates via
lookahead -- "X!Y::" (a name, then "::") is the new 3-part sheet+table
form; a bare "X!Y" keeps its original single-qualifier meaning, so
every formula written before this exists still parses identically.
CellNode/RangeNode gain an optional sheetQualifier field.
Workbook.resolveTableName(name, sheetName?) implements the resolution
policy; TableModel gains sheetName. precedentsOf() now also sets
homeTableId (previously only evaluateCell did), so graph edges use the
same same-sheet-preference resolution an evaluation would.

Store: table name uniqueness checks (addTable, renameObject) are now
scoped to the target sheet instead of the whole document. Point-mode's
qualifyRef() inserts the full "Blatt!Tabelle::" form only when the
clicked table's name is genuinely ambiguous and lives on a different
sheet than the editor; otherwise the simple form, unchanged.

200 tests passing (19 new), vue-tsc and eslint clean, verified live in
the running app: renamed a Blatt-2 table to the same name as Analyse's
seed "Umsatz", confirmed an unqualified reference resolves per-sheet,
an explicit sheet-qualified one always targets the named sheet, and
the original sheet's own formulas are unaffected.

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

src/engine/evaluator.ts

@@ -67,7 +67,9 @@ function evalScalar(node: Node, host: EngineHost): CellValue {
 
     case 'cell': {
       const tableId =
-        node.qualifier == null ? host.homeTableId : host.resolveTableName(node.qualifier);
+        node.qualifier == null
+          ? host.homeTableId
+          : host.resolveTableName(node.qualifier, node.sheetQualifier ?? null);
       if (!tableId) return new FormulaError('#REF', `unknown table '${node.qualifier}'`);
       return host.getComputed(tableId, node.col, node.row);
     }
@@ -104,7 +106,9 @@ function evalScalar(node: Node, host: EngineHost): CellValue {
 function evalArg(node: Node, host: EngineHost): FormulaError | CellValue[] {
   if (node.kind === 'range') {
     const tableId =
-      node.qualifier == null ? host.homeTableId : host.resolveTableName(node.qualifier);
+      node.qualifier == null
+        ? host.homeTableId
+        : host.resolveTableName(node.qualifier, node.sheetQualifier ?? null);
     if (!tableId) return new FormulaError('#REF', `unknown table '${node.qualifier}'`);
     return expandRange(node.start, node.end).map((c) => host.getComputed(tableId, c.col, c.row));
   }