The announce_table in RNS is only populated when transport mode is enabled.
On non-transport nodes, interface extraction always returned None, causing
announces to show "Unknown" interface.
Extract interface lookup into python/interface_lookup.py module that checks
announce_table first, then falls back to path_table (which is always
populated regardless of transport mode).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
