Add doc comments and TODO markers to SshSession::recv() and send()
explicitly marking them as Phase 1 stubs. Notes that call protocol
event bridging from SSH channels is planned for Phase 2/3.
Review found Phase 1 approved with minor issues. Created cleanup tasks:
- napi-identity-provider-wiring (bug: NAPI bypasses IdentityProvider)
- panic-free-static-config (code smell: panic/unwrap in production path)
- non-exhaustive-public-api (future-proofing public API types)
- adr-doc-comments (doc convention: ADR references in new modules)
- ssh-session-recv-stub-doc (documentation: mark stubs as planned)
