test: run integration suite against released live node

[Cryptoloveer]

Problem

The integration suite currently starts neighbour nodes from the same classpath under test. That preserves coverage but only validates the current implementation against itself, so compatibility regressions with the released network image can be missed.

Fix

• Keep the existing classpath neighbour mode as the default.
• Add a live neighbour mode that starts a fresh ghcr.io/attocash/node:live container.
• Reuse the generated local signer, genesis transaction, isolated database, and random node ports.
• Force the container onto the local test profile while preserving the released native binary.
• Pull the :live image for every run.
• Run classpath and live integration suites in parallel in pull-request CI.

Validation

This remains a draft until both CI matrix jobs run successfully. The classpath path is preserved and selected by default outside CI.

Closes #271.

[Cryptoloveer]

The classpath and :live paths are implemented as separate CI matrix jobs, with classpath remaining the default locally. The branch is synchronized with current main. Could a maintainer approve the fork workflow so both suites can validate the container networking and released-image compatibility before this is marked ready?