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/types.ts

@@ -70,19 +70,33 @@ export function parseKey(key: string): CellRef {
  * The document as seen by the engine. Implemented by the Vue store.
  *
  * The addressable unit is a **table** (a table object on a Numbers-style
- * canvas). Table names are unique across the whole document, so a qualified
- * reference like `Umsatz!B2` / `Umsatz::B2` resolves the same no matter which
- * sheet the formula or the target table sits on.
+ * canvas). Table names are only unique *per sheet* -- two different sheets
+ * may each hold a table called "Umsatz". An unqualified table reference
+ * (`Umsatz!B2` / `Umsatz::B2`, no sheet given) resolves to whichever table
+ * named "Umsatz" lives on the *same sheet* as the formula doing the
+ * referencing, falling back to the single document-wide match when the name
+ * isn't ambiguous there. The explicit 3-part form (`Analyse!Umsatz::B2`)
+ * disambiguates when it would otherwise be genuinely ambiguous (name used on
+ * two *other* sheets, neither of them the formula's own).
  */
 export interface EngineHost {
   /** Id of the table the formula currently being evaluated lives on. */
   homeTableId: string;
   /**
-   * Resolve a table *name* (as written in a formula) to its id. Matching is
-   * case-insensitive and tolerant of surrounding whitespace. Returns `null`
-   * for an unknown / deleted table.
+   * Resolve a table *name* (as written in a formula) to its id, optionally
+   * narrowed to a specific *sheet* name (the "Blatt!" part of a 3-part
+   * `Blatt!Tabelle::Zelle` reference). Matching is case-insensitive and
+   * tolerant of surrounding whitespace.
+   *
+   * - `sheetName` given: only a table with that name **on that sheet**
+   *   matches; otherwise `null` (including when the sheet itself is unknown).
+   * - `sheetName` omitted/`null`: matches a table by name anywhere in the
+   *   document. Exactly one match resolves as before. Multiple matches (the
+   *   name exists on more than one sheet) prefer a table on the same sheet
+   *   as {@link homeTableId}; if that still doesn't narrow it to one, `null`
+   *   (`#REF` -- the formula needs an explicit sheet qualifier).
    */
-  resolveTableName(name: string): string | null;
+  resolveTableName(name: string, sheetName?: string | null): string | null;
   /** Dimensions of a table, used for range clamping and #REF detection. */
   tableSize(tableId: string): { cols: number; rows: number } | null;
   /**