fix(aztec-up): allow verdaccio publish when npmjs uplink is offline

[AztecBot]

Summary

The aztec-up step in bootstrap.sh ci-full-no-test-cache stands up a local Verdaccio and publishes every @aztec/* and @noir-lang/* workspace package to it. When npmjs.org is briefly unreachable, Verdaccio caches the uplink as down for ~5 minutes (default fail_timeout) and refuses every publish in that window with:

npm error 503 Service Unavailable - PUT http://localhost:4873/@aztec%2f...
  one of the uplinks is down, refuse to publish

This bricked the merge-train CI run for merge-train/spartan (https://github.com/AztecProtocol/aztec-packages/actions/runs/25813115286, log 1778689953741897) even though the change itself (#23245 TxCollection refactor) is unrelated. The existing 3× retry in aztec-up/bootstrap.sh doesn't help because the cached uplink-down state outlives all retries — see the existing TODO on that line.

Fix

Add publish.allow_offline: true to the Verdaccio config. In Verdaccio's checkPackageRemote (see storage-utils.js), a non-404 uplink error normally produces UPLINK_OFFLINE_PUBLISH (the 503 above); with allow_offline set, that path resolves instead of rejecting, so transient npmjs hiccups no longer block local publish. Install/proxy behaviour for non-published packages is unchanged.

Test plan

• bootstrap.sh ci-full-no-test-cache passes through the aztec-up step
• Verified locally that Verdaccio v6.6.0 accepts the new config and that _isAllowPublishOffline reads publish.allow_offline (per node_modules/verdaccio/build/lib/storage.js). Full reproduction needs Docker which isn't available in this environment.

Full analysis: https://gist.github.com/AztecBot/9b0ccd4e3bbc1714bf490594037023ba

ClaudeBox log: https://claudebox.work/s/7ac785ba8051506f?run=1