Read berry restore registry like yarn does (#1017) (#1323)

* WIP: Fix berry restore registry lookup sources (#1017)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* Read berry restore registry like yarn does

Hosted yarn berry rollback, remove and the takeover restore read
only the project .yarnrc.yml's top-level npmRegistryServer. A
mirror set through npmScopes, YARN_NPM_REGISTRY_SERVER, a
parent-directory or home .yarnrc.yml, or a ${VAR:-default} value
was ignored. The restore then dropped the mirror's __archiveUrl
binding without a warning, and the next cold immutable install
failed YN0035.

The restore now resolves each package's registry the way yarn
merges its settings, and warns upstream_registry_fallback when
the registry cannot be determined.

Fixes #1017

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* Never expand set env vars into a registry URL

A checked-in .yarnrc.yml could name any variable of the
socket-patch process (a token) in npmRegistryServer. The restore
would then request, and on a failed lookup print, a URL carrying
it. A reference to a variable that is set is now treated as an
undeterminable registry. The restore falls back to the default
registry with upstream_registry_fallback, as the Bun and pnpm
settings readers already do. An unset variable's default is still
read the way yarn reads it.

The hosted-unwind test runner also clears YARN_NPM_REGISTRY_SERVER
and YARN_RC_FILENAME, so an ambient value can't steer the fixtures.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: mikolalysenko