SYNC_REQUEST 2 (#616)

* wip

* woohooo

* Plumtree gossip: don't subset REQUEST_SYNC fanout; make RequestSyncPacket.encode use const

* bloom -> gcs [wip]

* fix build

* fix broadcast

* prune old messages too

* faster sync

* prune better

* adjust parameters

* fix(sync): make cap a constant in GCSFilter.buildFilter to silence 'never mutated' warning

* fix(mesh): surface self-origin public messages recovered via sync; only ignore self when TTL != 0 in handleMessage

* sync: allow self messages via GCS restore and relax TTL==0 acceptance\n- Bypass dedup for self TTL==0 packets in handleReceivedPacket\n- Accept self TTL==0 in handleMessage and set nickname\n- Accept unknown senders for TTL==0 with anon# prefix to restore history

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

bitchat/Protocols/BitchatProtocol.swift

@@ -125,6 +125,7 @@ enum MessageType: UInt8 {
     case announce = 0x01        // "I'm here" with nickname
     case message = 0x02         // Public chat message  
     case leave = 0x03           // "I'm leaving"
+    case requestSync = 0x21     // GCS filter-based sync request (local-only)
     
     // Noise encryption
     case noiseHandshake = 0x10  // Handshake (init or response determined by payload)
@@ -138,6 +139,7 @@ enum MessageType: UInt8 {
         case .announce: return "announce"
         case .message: return "message"
         case .leave: return "leave"
+        case .requestSync: return "requestSync"
         case .noiseHandshake: return "noiseHandshake"
         case .noiseEncrypted: return "noiseEncrypted"
         case .fragment: return "fragment"