Friend-courier store-and-forward: mutual favorites carry sealed messages to offline peers

When a private message has no reachable transport, the router now seals it
to the recipient's Noise static key (new one-way Noise X pattern) and hands
the envelope to up to three connected mutual favorites. Couriers store the
opaque ciphertext under strict quotas (20 total, 5 per depositor, 16 KiB,
24 h) and hand it over when the recipient's announce matches a rotating
HMAC recipient tag; the recipient opens it and the message flows through
the normal private-message pipeline, so dedup and delivery acks just work.

- CourierEnvelope TLV + courierEnvelope (0x04) message type in BitFoundation
- Noise X one-way pattern reusing the existing handshake machinery,
  domain-separated by a courier prologue; sender identity authenticated
  via the ss DH (no forward secrecy - documented tradeoff)
- CourierStore with eviction, file persistence, and panic-wipe integration
- Rotating recipient tags (HMAC over epoch day) so carried envelopes don't
  correlate for observers who don't already know the recipient's key
- New "carried" delivery status with figure.walk glyph; header indicator
  while carrying mail for others
- Three-node end-to-end test ferrying packets through real BLEService
  instances, plus codec/crypto/store/router suites (986 tests green)

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

bitchatTests/ChatViewModelDeliveryStatusTests.swift

@@ -428,12 +428,13 @@ struct ChatViewModelDeliveryStatusTests {
     @Test @MainActor
     func statusRank_orderingIsCorrect() async {
         // This tests the implicit ordering used in refreshVisibleMessages
-        // failed < sending < sent < partiallyDelivered < delivered < read
+        // failed < sending < sent < carried < partiallyDelivered < delivered < read
 
         let statuses: [DeliveryStatus] = [
             .failed(reason: "test"),
             .sending,
             .sent,
+            .carried,
             .partiallyDelivered(reached: 1, total: 3),
             .delivered(to: "B", at: Date()),
             .read(by: "C", at: Date())
@@ -446,9 +447,10 @@ struct ChatViewModelDeliveryStatusTests {
             case .failed: #expect(index == 0)
             case .sending: #expect(index == 1)
             case .sent: #expect(index == 2)
-            case .partiallyDelivered: #expect(index == 3)
-            case .delivered: #expect(index == 4)
-            case .read: #expect(index == 5)
+            case .carried: #expect(index == 3)
+            case .partiallyDelivered: #expect(index == 4)
+            case .delivered: #expect(index == 5)
+            case .read: #expect(index == 6)
             }
         }
     }