Rewrite e2e tests for ADR-002 direct pub/sub flow

[swarna1101]

e2e suite was removed during the ADR-002 CLI rewrite. Needs new tests covering session creation, direct node subscribe/publish via gRPC CommandStream.

[linear]

OPT-521

[Seqo01]

For #101, should the E2E suite be hermetic, using an in-process fake /api/v1/session service and fake gRPC CommandStream, or should it run against the locally deployed Docker proxy/P2P stack from the public dev setup?