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/Mocks/MockIdentityManager.swift

@@ -11,18 +11,11 @@ import BitFoundation
 @testable import bitchat
 
 final class MockIdentityManager: SecureIdentityStateManagerProtocol {
-    private let keychain: KeychainManagerProtocol
     private var blockedFingerprints: Set<String> = []
     private var blockedNostrPubkeys: Set<String> = []
     private var socialIdentities: [String: SocialIdentity] = [:]
-    
-    init(_ keychain: KeychainManagerProtocol) {
-        self.keychain = keychain
-    }
-    
-    func loadIdentityCache() {}
-    
-    func saveIdentityCache() {}
+
+    init(_: KeychainManagerProtocol) {}
     
     func forceSave() {}
     
@@ -45,12 +38,6 @@ final class MockIdentityManager: SecureIdentityStateManagerProtocol {
         }
     }
     
-    func getFavorites() -> Set<String> {
-        Set()
-    }
-    
-    func setFavorite(_ fingerprint: String, isFavorite: Bool) {}
-    
     func isFavorite(fingerprint: String) -> Bool {
         false
     }
@@ -99,9 +86,7 @@ final class MockIdentityManager: SecureIdentityStateManagerProtocol {
     }
     
     func registerEphemeralSession(peerID: PeerID, handshakeState: HandshakeState) {}
-    
-    func updateHandshakeState(peerID: PeerID, state: HandshakeState) {}
-    
+
     func clearAllIdentityData() {}
     
     func removeEphemeralSession(peerID: PeerID) {}
@@ -139,10 +124,6 @@ final class MockIdentityManager: SecureIdentityStateManagerProtocol {
         !(vouchesByVouchee[fingerprint] ?? []).isEmpty
     }
 
-    func effectiveTrustLevel(for fingerprint: String) -> TrustLevel {
-        socialIdentities[fingerprint]?.trustLevel ?? .unknown
-    }
-
     func lastVouchBatchSent(to fingerprint: String) -> Date? {
         vouchBatchSentAt[fingerprint]
     }