feat(mesh): show federated Archipelago nodes on the Mesh Map

Peers that opt in via a new "Share Location" toggle in Settings
(server.set-location RPC) get plotted on other trusted peers' Mesh Map
with a distinct Archy-logo marker, separate from raw LoRa radio peers.
Location is persisted locally, carried in NodeStateSnapshot, and
propagated through federation sync/delta like other node state.

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

core/archipelago/src/data_model.rs

@@ -61,6 +61,18 @@ pub struct ServerInfo {
     /// True if this node's keys are derived from a BIP-39 seed.
     #[serde(rename = "seed-backed", default)]
     pub seed_backed: bool,
+    /// This node's own physical location, for the Mesh Map — opt-in only
+    /// (see `share_location`), set via `server.set-location`. `None` until
+    /// the user sets one, regardless of `share_location`.
+    #[serde(default)]
+    pub lat: Option<f64>,
+    #[serde(default)]
+    pub lon: Option<f64>,
+    /// Whether `lat`/`lon` should be included in the state snapshot we send
+    /// to trusted federation peers (so they can plot us on their Mesh Map).
+    /// Defaults to false — never shared unless explicitly turned on.
+    #[serde(rename = "share-location", default)]
+    pub share_location: bool,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
@@ -347,6 +359,9 @@ impl DataModel {
                 wifi_ssids: vec![],
                 zram_enabled: false,
                 seed_backed: false,
+                lat: None,
+                lon: None,
+                share_location: false,
             },
             package_data: HashMap::new(),
             peer_health: HashMap::new(),