Fix accidental /// comments and a docs typo (#64287)

## Objective

Fix small comment/docs typos left out of #64282.

## Solution

- Replace accidental Rust-style `///` comments with `//` in
`assets/settings/default.json` (`git_panel.tree_view` and
`git.gutter_debounce`)
- Fix typo in `docs/src/visual-customization.md`:
`"enable_language_server" if false` ? `is false`

## Testing

Comment/docs-only changes; no runtime behavior change.

---

Release Notes:

- N/A

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

docs/src/visual-customization.md

@@ -370,7 +370,7 @@ TBD: Centered layout related settings
   "global_lsp_settings": {
     // Show/hide the LSP button in the status bar.
     // Activity from the LSP is still shown.
-    // Button is not shown if "enable_language_server" if false.
+    // Button is not shown if "enable_language_server" is false.
     "button": true
   },
 ```