Add BLE file transfer support and media UX

bitchat/Utils/FileTransferLimits.swift

@@ -0,0 +1,15 @@
+import Foundation
+
+/// Centralized thresholds for Bluetooth file transfers to keep payload sizes sane on constrained radios.
+enum FileTransferLimits {
+    /// Absolute ceiling enforced for any file payload (voice, image, other).
+    static let maxPayloadBytes: Int = 8 * 1024 * 1024 // 8 MiB
+    /// Voice notes stay small for low-latency relays.
+    static let maxVoiceNoteBytes: Int = 2 * 1024 * 1024 // 2 MiB
+    /// Compressed images after downscaling should comfortably fit under this budget.
+    static let maxImageBytes: Int = 4 * 1024 * 1024 // 4 MiB
+
+    static func isValidPayload(_ size: Int) -> Bool {
+        size <= maxPayloadBytes
+    }
+}