Feat/mesh robustness efficiency (#451)

* chat: de-dup private chats across ephemeral/stable IDs; prefer most advanced delivery status\n\n- Fixes LazyVStack duplicate ID warnings and blank row in PM\n- Merges messages by id from ephemeral and Noise-key stores\n- Chooses read > delivered > partiallyDelivered > sent > sending > failed (newer wins on tie)\n- Ensures status icon updates immediately without waiting for another send\n- Adds exhaustive handling for DeliveryStatus in ranking

* logging: reduce noisy info logs to debug; keep errors/warnings\n\n- Downgrade routing/ACK/subscription/connect logs to debug\n- Retain security/fingerprint/keychain info logs\n- Keep errors and warnings intact\n\ndocs: add docs/privacy-assessment.md covering BLE privacy, routing TTL/jitter, Nostr E2E gift wraps, ACK throttling, and logging posture

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

bitchat/Nostr/NostrRelayManager.swift

@@ -97,7 +97,7 @@ class NostrRelayManager: ObservableObject {
     ) {
         messageHandlers[id] = handler
         
-        SecureLogger.log("📡 Setting up subscription '\(id)' with filter - kinds: \(filter.kinds ?? []), since: \(filter.since ?? 0)", 
+        SecureLogger.log("📡 Subscribing to Nostr filter id=\(id) kinds=\(filter.kinds ?? []) since=\(filter.since ?? 0)", 
                         category: SecureLogger.session, level: .debug)
         
         let req = NostrRequest.subscribe(id: id, filters: [filter])