fix(vfs): poll for changes when the OS file watcher cannot start (#906)

Opening a project failed outright when the OS file watcher could not start (inotify limits used up, a file system without change notifications). The watcher now falls back to polling the same non-ignored directories every 2s, per directory unless flat so excluded trees like `node_modules` and `target` are not rescanned, and the project opens with an "External file changes sync may be slow" warning that gives the reason. Directory mtime changes seen only by polling are dropped so folders are not reported as modified.

Fixes #891.

Co-authored-by: azeemhassni <[email protected]>

src/platform/locales/text/zh.json

@@ -5547,5 +5547,6 @@
   "Passed as --settings; empty keeps DJANGO_SETTINGS_MODULE or the default in manage.py": "作为 --settings 传入；留空则沿用 DJANGO_SETTINGS_MODULE 或 manage.py 中的默认值",
   "e.g. --keepdb --parallel": "例如 --keepdb --parallel",
   "select files in a git repository to shelve": "请选择 Git 仓库中的文件以搁置更改",
-  "select files from a single git repository to shelve": "请一次只选择同一个 Git 仓库中的文件以搁置更改"
+  "select files from a single git repository to shelve": "请一次只选择同一个 Git 仓库中的文件以搁置更改",
+  "External file changes sync may be slow": "外部文件更改同步可能较慢"
 }