Remove noise service exposure; single-owner selection state

Transport callers no longer reach the raw NoiseEncryptionService:
getNoiseService() is deleted in favor of narrow purpose-named Transport
methods (session public key, identity fingerprint, static/signing keys,
sign/verify, callback installation). VerificationService now reaches
crypto through the transport, so it can no longer pin a stale service
across a panic reset. myPeerID/myNickname become private(set); the
existing setNickname mutator is the sole nickname path.

ConversationStore is now the sole owner of private-chat selection:
PrivateChatManager.selectedPeer is a published read-only mirror, and
startChat/endChat mutate through the store intent. The bridge method
and its five call sites are deleted, removing a latent bug where a
stale manager selection pushed back into the store could resurrect a
just-removed conversation.

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

bitchat/App/AppRuntime.swift

@@ -105,7 +105,7 @@ final class AppRuntime: ObservableObject {
 
         started = true
         NotificationDelegate.shared.runtime = self
-        VerificationService.shared.configure(with: chatViewModel.meshService.getNoiseService())
+        VerificationService.shared.configure(with: chatViewModel.meshService)
         announceInitialTorStatusIfNeeded()
 
         Task(priority: .utility) { [weak self] in