## Objective

`file_scan_exclusions` replaces the defaults instead of adding to them,
so excluding one extra directory means restating all eleven default
globs and never picking up defaults added in later Zed releases.

## Solution

`file_scan_exclusions` now accepts the `"..."` entry, which expands to
the value it overrides, so `["**/node_modules", "..."]` adds to the
inherited globs instead of replacing them. Entries listed by name keep
their position, and leaving `"..."` out still replaces the list
outright, so existing settings behave exactly as they do today.

## Testing

- Four unit tests in `crates/settings_content/src/project.rs` cover
splicing versus replacing, accumulation across successive layers, and
edge cases: a repeated `"..."`, an empty list clearing the value, and a
bare `["..."]` leaving it unchanged.
- To check by hand: set `"file_scan_exclusions": ["**/node_modules",
"..."]` in user settings and confirm `node_modules` disappears from the
project panel and file finder while `.git` and `.DS_Store` stay
excluded. Remove `"..."` and confirm only `node_modules` is excluded.
Repeat in a project's `.zed/settings.json` to confirm it splices the
resolved user settings rather than the defaults.
- Tested on macOS. This is platform-independent settings-merge logic
with no OS-specific code paths, so I did not test Linux or Windows.

## Self-Review Checklist:

- [x] I’ve reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed’s UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

---

Release Notes:

- Added support for the `"..."` entry in `file_scan_exclusions`. Custom
exclusions can now extend the defaults instead of replacing them.