Wire the `QUIC` transport feature

Summary

The QUIC machinery is fully implemented but unreachable in production:

• QuicUpgradeBehaviour (431 lines, complete port of Charon's upgrade loop) is always installed, but the node hardcodes NodeType::TCP (TODO(#402 part B)), so with_quic_enabled(true) is never reached and the upgrade loop early-returns every tick.
• Feature::Quic is declared, parsed, and defaulted (Alpha, matching Charon) — but never queried: feature_set.enabled(Feature::Quic) has zero call sites. --feature-set-enable=quic and run's --p2p-udp-address are silently inert.
• Charon's wiring is one conditional: app.go#L368-L372 picks NodeTypeQUIC vs NodeTypeTCP off the featureset.
• Related dead code: is_quic_enabled has zero call sites; quic_upgrade.rs has no test module (Charon has TestNewQUICHost plus QUIC-host test helpers).

Proposed change

• Branch NodeType on feature_set.enabled(Feature::Quic) in wire_p2p, mirroring Charon.
• Fix the server-path with_quic_enabled omission — covered by the transport unification (draft 15b), which should land first or together.
• Remove or use is_quic_enabled; add QUIC tests.

Acceptance

--feature-set-enable=quic on run produces a node that listens on the configured UDP address and upgrades established TCP connections to QUIC (observable via the upgrade behaviour's logs/metrics in a two-node test).