refactor(daemon): introduce AutoContext, extract relay helpers

- Add AutoContext struct bundling shared state (global, cfg, metrics,
  peers, routes, route_updates_tx, node_state, tun_capable); all
  internal auto-mode functions now take Arc<AutoContext> instead of
  8-11 individual arguments

- Extract spawn_source_to_peer_bidi_bridge and
  spawn_peer_announcement_forwarder from relay.rs as pub(crate)
  non-generic helpers operating on erased types; auto.rs uses these
  instead of copy-pasted inline blocks

- Remove dead route_updates receiver parameter from auto::run; callers
  obtain fresh receivers via ctx.route_updates_tx.subscribe()

- Remove #[allow(clippy::too_many_arguments)] suppressions where fixed

Net: -298 lines across three files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: maxholman