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/ChatNostrCoordinatorContextTests.swift

@@ -70,7 +70,6 @@ private final class MockChatNostrContext: ChatNostrContext {
     private(set) var mentionCheckedMessageIDs: [String] = []
     private(set) var hapticMessageIDs: [String] = []
 
-    func handlePublicMessage(_ message: BitchatMessage) { handledPublicMessages.append(message) }
     func handlePublicMessage(_ message: BitchatMessage, powBits: Int) { handledPublicMessages.append(message) }
     func checkForMentions(_ message: BitchatMessage) { mentionCheckedMessageIDs.append(message.id) }
     func sendHapticFeedback(for message: BitchatMessage) { hapticMessageIDs.append(message.id) }
@@ -214,8 +213,6 @@ private final class MockChatNostrContext: ChatNostrContext {
 
     // Favorites & notifications
     var favoriteRelationshipsByNoiseKey: [Data: FavoritesPersistenceService.FavoriteRelationship] = [:]
-    private(set) var addedFavorites: [(noiseKey: Data, nostrPublicKey: String?, nickname: String)] = []
-    private(set) var postedLocalNotifications: [(title: String, body: String, identifier: String)] = []
     private(set) var geohashActivityNotifications: [(geohash: String, bodyPreview: String)] = []
 
     func favoriteRelationship(forNoiseKey noiseKey: Data) -> FavoritesPersistenceService.FavoriteRelationship? {
@@ -226,14 +223,6 @@ private final class MockChatNostrContext: ChatNostrContext {
         Array(favoriteRelationshipsByNoiseKey.values)
     }
 
-    func addFavorite(noiseKey: Data, nostrPublicKey: String?, nickname: String) {
-        addedFavorites.append((noiseKey, nostrPublicKey, nickname))
-    }
-
-    func postLocalNotification(title: String, body: String, identifier: String) {
-        postedLocalNotifications.append((title, body, identifier))
-    }
-
     func notifyGeohashActivity(geohash: String, bodyPreview: String) {
         geohashActivityNotifications.append((geohash, bodyPreview))
     }
@@ -250,24 +239,6 @@ private func drainMainQueue() async {
     }
 }
 
-private func makeFavoriteRelationship(
-    noiseKey: Data,
-    nostrPublicKey: String? = nil,
-    nickname: String = "alice",
-    isFavorite: Bool = false,
-    theyFavoritedUs: Bool = false
-) -> FavoritesPersistenceService.FavoriteRelationship {
-    FavoritesPersistenceService.FavoriteRelationship(
-        peerNoisePublicKey: noiseKey,
-        peerNostrPublicKey: nostrPublicKey,
-        peerNickname: nickname,
-        isFavorite: isFavorite,
-        theyFavoritedUs: theyFavoritedUs,
-        favoritedAt: Date(timeIntervalSince1970: 0),
-        lastUpdated: Date(timeIntervalSince1970: 0)
-    )
-}
-
 // MARK: - Coordinator Tests Against Mock Context
 
 /// Exercises `ChatNostrCoordinator` against `MockChatNostrContext` with no