docs(browser): fix incomplete and typo comments in Mouse.ts

getCoords had a truncated comment ("if there are no valid") and a typo
("addition" vs "additional") in the selection precision note. Complete
the char-size guard comment and fix the selection wording.

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

src/browser/input/Mouse.ts

@@ -31,7 +31,7 @@ export function getCoordsRelativeToElement(window: Pick<Window, 'getComputedStyl
  * select that cell and the right half will select the next cell.
  */
 export function getCoords(window: Pick<Window, 'getComputedStyle'>, event: Pick<MouseEvent, 'clientX' | 'clientY'>, element: HTMLElement, colCount: number, rowCount: number, hasValidCharSize: boolean, cssCellWidth: number, cssCellHeight: number, isSelection?: boolean): [number, number] | undefined {
-  // Coordinates cannot be measured if there are no valid
+  // Coordinates cannot be measured if there is no valid character size.
   if (!hasValidCharSize) {
     return undefined;
   }
@@ -45,7 +45,7 @@ export function getCoords(window: Pick<Window, 'getComputedStyle'>, event: Pick<
   coords[1] = Math.ceil(coords[1] / cssCellHeight);
 
   // Ensure coordinates are within the terminal viewport. Note that selections
-  // need an addition point of precision to cover the end point (as characters
+  // need an additional point of precision to cover the end point (as characters
   // cover half of one char and half of the next).
   coords[0] = Math.min(Math.max(coords[0], 1), colCount + (isSelection ? 1 : 0));
   coords[1] = Math.min(Math.max(coords[1], 1), rowCount);