Encrypt private media before BLE fragmentation (#1434)

Closes the last cleartext private-content path over BLE: private DM images/voice were sent as plaintext signed fileTransfer packets, TTL-relayed across the mesh, so every relay saw the full bytes. Now the complete BitchatFilePacket is encrypted as a single Noise AEAD message (inner type 0x20, matching Android) and the opaque ciphertext is fragmented. Adds an authenticated in-session capability proof (0x21 TLV: capabilities + Ed25519 key), TOFU-style downgrade pinning, a per-send consent dialog for the signed-cleartext fallback to legacy peers, and a cancellation/admission registry so cancel/delete cannot race a deferred cleartext send.

Android wire constants (0x20 / 0x21 / capability bit 8) confirmed shipping. The 256-fragment preflight cap applies only to the directed fileTransfer migration fallback; encrypted media to capable peers uses the full receiver ceiling.

Rebased over #1428/#1349: identity reads go through BLELocalIdentityStateStore; the session-bound authenticated signing-key check and the announce-path TOFU pin are kept as complementary checks. Full local suite green (1744+197 tests).

bitchatTests/Services/BLEOutboundFragmentTransferSchedulerTests.swift

@@ -20,6 +20,24 @@ struct BLEOutboundFragmentTransferSchedulerTests {
         }
     }
 
+    @Test
+    func explicitTransferIDReservesEncryptedPrivateFileFragments() {
+        var scheduler = BLEOutboundFragmentTransferScheduler()
+        let request = makeRequest(
+            type: MessageType.noiseEncrypted.rawValue,
+            transferId: "private-media"
+        )
+
+        let result = scheduler.submit(request, maxConcurrentTransfers: 1)
+
+        if case let .start(_, reservedTransferId) = result {
+            #expect(reservedTransferId == "private-media")
+            #expect(scheduler.activeCount == 1)
+        } else {
+            Issue.record("Expected encrypted private media to reserve its progress slot")
+        }
+    }
+
     @Test
     func submitQueuesFileTransferWhenSlotsAreFull() {
         var scheduler = BLEOutboundFragmentTransferScheduler()