feat(mesh): Meshtastic RSSI/SNR + peer-location map wiring (backlog #14/#15, part 1)

Backend: parse_mesh_packet now decodes MeshPacket.rx_snr (field 8, float) and
rx_rssi (field 12, int32), and a new POSITION_APP branch decodes Position.
latitude_i/longitude_i (fields 1/2, sfixed32) -- all field numbers confirmed
against the canonical meshtastic/protobufs mesh.proto, not guessed. Threaded
through ParsedContact -> refresh_contacts -> MeshPeer (mirroring how
pkc_capable was wired for #17), so mesh.peers now surfaces real rssi/snr/lat/
lon instead of always-null. Fixed a real bug found along the way:
update_node_info's unconditional contact replace would have silently wiped
any already-tracked signal/position data on the next NodeInfo packet -- now
preserves it.

Frontend: mesh.ts's updateNodePositionsFromPeers() feeds real position data
into the SAME nodePositions map MeshMap.vue already renders from (parallel to
the existing Coordinate/Alert-message path) -- MeshMap.vue itself needed zero
changes, it was already built for this.

105/105 mesh tests pass (4 new: rx_snr/rx_rssi decode, position decode +
incomplete-field handling, full packet_to_inbound_frame integration).

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

neode-ui/src/stores/mesh.ts

@@ -38,6 +38,10 @@ export interface MeshPeer {
   hops: number
   last_advert?: number
   reachable?: boolean
+  /** Last known position (degrees), from a Meshtastic POSITION_APP broadcast.
+   *  Absent until the peer has shared one. */
+  lat?: number | null
+  lon?: number | null
 }
 
 export interface MeshChannel {
@@ -215,6 +219,7 @@ export const useMeshStore = defineStore('mesh', () => {
         method: 'mesh.peers',
       })
       peers.value = res.peers
+      updateNodePositionsFromPeers(res.peers)
     } catch (err: unknown) {
       error.value = err instanceof Error ? err.message : 'Failed to fetch mesh peers'
     }
@@ -298,6 +303,27 @@ export const useMeshStore = defineStore('mesh', () => {
     }
   }
 
+  /** Feed real Meshtastic POSITION_APP broadcasts into the same map the
+   *  manually-shared Coordinate/Alert messages already populate — MeshMap.vue
+   *  needs no changes, it already renders from `nodePositions`. Uses
+   *  `last_heard` as the freshness timestamp, same comparison pattern as
+   *  `updateNodePositionsFromMessages`, so a peer position never clobbers a
+   *  more-recently-shared coordinate message and vice versa. */
+  function updateNodePositionsFromPeers(peerList: MeshPeer[]) {
+    for (const peer of peerList) {
+      if (typeof peer.lat !== 'number' || typeof peer.lon !== 'number') continue
+      const existing = nodePositions.value.get(peer.contact_id)
+      if (!existing || peer.last_heard > existing.timestamp) {
+        nodePositions.value.set(peer.contact_id, {
+          lat: peer.lat,
+          lng: peer.lon,
+          label: peer.advert_name,
+          timestamp: peer.last_heard,
+        })
+      }
+    }
+  }
+
   function getNodePositions(): Map<number, NodePosition> {
     return nodePositions.value
   }