## Objective

The doc comment links for `Settings::PRESERVED_KEYS` point to
`[FileContent](Self::FileContent)` but that associated type was removed
by the settings refactor in
https://github.com/zed-industries/zed/pull/38367.
`Settings::from_settings` now takes `&SettingsContent` directly. The
dead link causes `rustdoc::broken_intra_doc_links` warnings when
building docs for the `settings` crate:

```
warning: unresolved link to `Self::FileContent`
  --> crates/settings/src/settings_store.rs:61:53
    |
61 |     /// The name of the keys in the [`FileContent`](Self::FileContent) that should
    |                                                     ^^^^^^^^^^^^^^^^^ the trait `Settings` has no associated item named `FileContent`
```

Fixes #57310

## Solution

Replaced both `[FileContent](Self::FileContent)` occurrences in
`crates/settings/src/settings_store.rs` with `[SettingsContent]`, which
is already in scope via the existing `use` at the top of the file and
resolves correctly. Docs-only change, no runtime behavior change.

## Testing

- Verified with `cargo doc -p settings --no-deps`, which now completes
without any `broken_intra_doc_links` warnings (previously emitted two).
- No runtime code touched — doc comments only, so no other testing
applies.

## 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:

- N/A