REL-10583: Resolve @symphony packages via sym-npmjs-virtual

[andrewjohns-sym]

Follow-up to #418.

Drops the explicit @symphony:registry pin to c9-npm-us-east4 from .npmrc, so that all dependency resolution — including @symphony/* packages — goes through sym-npmjs-virtual.

Publication is unaffected: the generated package's publishConfig continues to select c9-npm-us-east4, so sym-npmjs-virtual is read-only and c9-npm-us-east4 remains publish-only.

.npmrc after this change:

registry=https://us-east4-npm.pkg.dev/sym-prod-mr-tools-01/sym-npmjs-virtual/

The auth token lines in the Jenkinsfile still cover both registries, so no credential change is needed.

🤖 Generated with Claude Code

[linux-foundation-easycla]

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