UI: diversify peer colors; smarter geo notifications; 21m live location (#531)

- Use minimal-distance hue palette for mesh and geohash lists; align chat sender colors with list palette.
- Add foreground geo notifications for different channels; deep-link to bitchat://geohash/<gh>; per-geohash 60s cooldown; respect self/blocks.
- Global geohash sampling runs outside the sheet; delegate handles deeplinks and suppresses when already in-channel.
- Switch location channel sheet to continuous CoreLocation with 21m distance filter; add config knob.
- Only link geohash hashtags when standalone (no @name#abcd or word#abcd).
- Include mesh-reachable peers in mesh counts and in "bitchatters nearby" notification.
- Add TransportConfig knobs for palette and geo notifications.

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Services/NotificationService.swift

@@ -90,6 +90,15 @@ class NotificationService {
         }
     }
     
+    // Geohash public chat notification with deep link to a specific geohash
+    func sendGeohashActivityNotification(geohash: String, titlePrefix: String = "#", bodyPreview: String) {
+        let title = "\(titlePrefix)\(geohash)"
+        let identifier = "geo-activity-\(geohash)-\(Date().timeIntervalSince1970)"
+        let deeplink = "bitchat://geohash/\(geohash)"
+        let userInfo: [String: Any] = ["deeplink": deeplink]
+        sendLocalNotification(title: title, body: bodyPreview, identifier: identifier, userInfo: userInfo)
+    }
+
     func sendNetworkAvailableNotification(peerCount: Int) {
         let title = "👥 bitchatters nearby!"
         let body = peerCount == 1 ? "1 person around" : "\(peerCount) people around"