Remove dead code found by full Periphery audit; add scan config + advisory CI (#1410)

Periphery 3.7.4 audit of both schemes (macOS + iOS, intersected so
platform-specific code is never touched), with test targets indexed and
the share extension built. 277 dead declarations removed or demoted:
dead forwarding wrappers (ChatViewModel+Nostr/+PrivateChat), removed-
feature remnants (autocomplete command suggestions, back-swipe tuning,
MediaSendError, GeohashParticipantTracker), unused Tor dormancy
bindings, assign-only properties, unused parameters (renamed to _), and
redundant public accessibility. 13 orphaned localization keys deleted
across all 29 locales (old pre-#1392 location-notes UI, app_info
warnings).

Two real tests were flagged as unused because they never ran: Swift
Testing methods missing @Test (NostrProtocolTests.
testAckRoundTripNIP44V2_Delivered, NotificationStreamAssemblerTests.
testAssemblesCompressedLargeFrame). Re-armed both; they pass.

Deliberately kept, now recorded in .periphery.baseline.json: iOS-only
code invisible to the CI macOS scan, C FFI signatures, keep-alive
NWPathMonitor reference, InboundEventKey.eventID (dedup semantics),
wifiBulk capability bit (reserved for Wi-Fi bulk work, used by
BitFoundation package tests), and the String secureClear cluster
(exercised by package tests).

New: .periphery.yml config and an advisory Dead Code CI job (mirrors
the SwiftLint precedent from #1361) that fails on findings not in the
committed baseline.

Verified: full macOS app suite, BitFoundation (119) and BitLogger (13)
package tests green; periphery scan --strict exits clean.

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchatTests/TestUtilities/TestConstants.swift

@@ -25,9 +25,5 @@ struct TestConstants {
     static let testNickname4 = "David"
     
     static let testMessage1 = "Hello, World!"
-    static let testMessage2 = "How are you?"
-    static let testMessage3 = "This is a test message"
     static let testLongMessage = String(repeating: "This is a long message. ", count: 100)
-    
-    static let testSignature = Data(repeating: 0xAB, count: 64)
 }

bitchatTests/TestUtilities/TestHelpers.swift

@@ -12,20 +12,7 @@ import BitFoundation
 @testable import bitchat
 
 final class TestHelpers {
-    
-    // MARK: - Key Generation
-    
-    static func generateTestKeyPair() -> (privateKey: Curve25519.KeyAgreement.PrivateKey, publicKey: Curve25519.KeyAgreement.PublicKey) {
-        let privateKey = Curve25519.KeyAgreement.PrivateKey()
-        let publicKey = privateKey.publicKey
-        return (privateKey, publicKey)
-    }
-    
-    static func generateTestIdentity(peerID: String, nickname: String) -> (peerID: String, nickname: String, privateKey: Curve25519.KeyAgreement.PrivateKey, publicKey: Curve25519.KeyAgreement.PublicKey) {
-        let (privateKey, publicKey) = generateTestKeyPair()
-        return (peerID: peerID, nickname: nickname, privateKey: privateKey, publicKey: publicKey)
-    }
-    
+
     // MARK: - Message Creation
     
     static func createTestMessage(
@@ -78,11 +65,7 @@ final class TestHelpers {
         }
         return data
     }
-    
-    static func generateTestPeerID() -> String {
-        return "PEER" + UUID().uuidString.prefix(8)
-    }
-    
+
     // MARK: - Async Helpers
     
     static func waitFor(_ condition: @escaping () -> Bool, timeout: TimeInterval = TestConstants.defaultTimeout) async throws {
@@ -110,32 +93,10 @@ final class TestHelpers {
         }
         return true
     }
-    
-    static func expectAsync<T>(
-        timeout: TimeInterval = TestConstants.defaultTimeout,
-        operation: @escaping () async throws -> T
-    ) async throws -> T {
-        return try await withThrowingTaskGroup(of: T.self) { group in
-            group.addTask {
-                return try await operation()
-            }
-            
-            group.addTask {
-                try await sleep(1)
-                throw TestError.timeout
-            }
-            
-            let result = try await group.next()!
-            group.cancelAll()
-            return result
-        }
-    }
 }
 
 enum TestError: Error {
     case timeout
-    case unexpectedValue
-    case testFailure(String)
 }
 
 // MARK: - Private chat seeding (ConversationStore migration)
@@ -164,18 +125,6 @@ extension ChatViewModel {
         }
     }
 
-    /// Test-only replacement for `messages.removeAll()`: empties a public
-    /// channel's conversation.
-    @MainActor
-    func clearPublicMessages(for channel: ChannelID = .mesh) {
-        conversations.clear(ConversationID(channelID: channel))
-    }
-
-    /// Test-only: drops every private chat and unread flag.
-    @MainActor
-    func clearAllPrivateChats() {
-        conversations.removeAllDirectConversations()
-    }
 }
 
 func sleep(_ seconds: TimeInterval) async throws {