fix(addon-search): reject startCol equal to terminal column count

Valid column indices are 0 through cols - 1. The previous check used
startCol > cols, so on an 80-column terminal column 80 was accepted while
column 100 correctly threw. Use >= so the out-of-range guard matches the
documented error for invalid search positions.

Co-authored-by: Cursor <cursoragent@cursor.com>

addons/addon-search/src/SearchEngine.ts

@@ -60,7 +60,7 @@ export class SearchEngine {
       this._terminal.clearSelection();
       return undefined;
     }
-    if (startCol > this._terminal.cols) {
+    if (startCol >= this._terminal.cols) {
       throw new Error(`Invalid col: ${startCol} to search in terminal of ${this._terminal.cols} cols`);
     }