docs: recommend install-strategy=linked to catch phantom dependencies (#9678)

Encourages package authors to develop under `install-strategy=linked` to
surface undeclared ("phantom") dependencies before publishing.

Under the default hoisted `node_modules`, a package can `import` a
dependency it never declared and still resolve it: a transitive
dependency hoisted alongside it (or a workspace root's `node_modules`)
happens to satisfy the import. That undeclared dependency passes the
author's own build silently, then fails for a consumer who installs the
package on its own. The linked (isolated) layout exposes only a
package's declared dependencies, so such an import can fail at the
author's build instead of shipping broken.

The change documents this in two places:

- The `install-strategy` entry in the config reference now recommends
that authors use `--install-strategy=linked` during development,
cross-linked to the developers guide.
- The Developers guide gains a "Catching undeclared ("phantom")
dependencies" section under "Before Publishing", with a note that this
is one check — a dependency satisfied by a `devDependency` or a
workspace root's `node_modules` can still resolve locally — alongside
auditing the dependencies the published package actually uses.

This is documentation-only; the config reference text is generated from
the `install-strategy` definition description.

## References

Closes #9675