network: per-peer connection badge (direct/relay, RTT, loss, bitrate)

Answer "am I actually P2P right now?" per peer. A 1 Hz session task
snapshots the selected QUIC path of every live audio connection
(IrohTransport::connection_stats), core::connstats::derive turns
consecutive snapshots into RTT/loss/bitrate (path switches and counter
resets invalidate the rate window), and the peer card shows a
Direct/Relay badge with a hover tooltip for address, loss, and up/down
bitrate. No new dependencies, no wire change.

Loopback-integration-tested against real iroh endpoints; not yet
field-verified on a 2-machine call (FEATURES.md row marked 🧪).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/FEATURES.md

@@ -102,6 +102,7 @@ covers internals). When you ship a feature, add it here.
 | iroh QUIC transport | ✅ | |
 | Network mode picker | ✅ | `RelayNoDiscovery` (default), `N0Full`, `DirectOnly`. Takes effect next join. |
 | Retained-address reconnect | ✅ | Dials last-known full addr before falling back to bare id. |
+| Per-peer connection badge (direct/relay + RTT, hover for addr/loss/bitrate) | 🧪 | Peer-card badge fed by a 1 Hz poll of the live audio link's selected QUIC path (`connection_stats` → `core::connstats::derive`). Loopback-integration-tested; not field-tested on a real 2-machine call. |
 | Reconnect + eviction model | ✅ | Incl. two-outage reconnect-eviction fix + regression test. |
 | Self-hosted relay | ❌ | Decided against — rely on n0 relays, `RelayNoDiscovery` default. |