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>

bitchat/ViewModels/Extensions/ChatViewModel+Nostr.swift

@@ -35,11 +35,6 @@ extension ChatViewModel {
         nostrCoordinator.inbound.handleNostrEvent(event)
     }
 
-    @MainActor
-    func subscribeToGeoChat(_ ch: GeohashChannel) {
-        nostrCoordinator.subscriptions.subscribeToGeoChat(ch)
-    }
-
     @MainActor
     func handleGiftWrap(_ giftWrap: NostrEvent, id: NostrIdentity) {
         nostrCoordinator.inbound.handleGiftWrap(giftWrap, id: id)
@@ -55,21 +50,11 @@ extension ChatViewModel {
         nostrCoordinator.subscriptions.beginGeohashSampling(for: geohashes)
     }
 
-    @MainActor
-    func subscribe(_ gh: String) {
-        nostrCoordinator.subscriptions.subscribe(gh)
-    }
-
     @MainActor
     func subscribeNostrEvent(_ event: NostrEvent, gh: String) {
         nostrCoordinator.presence.subscribeNostrEvent(event, gh: gh)
     }
 
-    @MainActor
-    func cooldownPerGeohash(_ gh: String, content: String, event: NostrEvent) {
-        nostrCoordinator.presence.cooldownPerGeohash(gh, content: content, event: event)
-    }
-
     @MainActor
     func endGeohashSampling() {
         nostrCoordinator.subscriptions.endGeohashSampling()
@@ -80,35 +65,11 @@ extension ChatViewModel {
         nostrCoordinator.subscriptions.setupNostrMessageHandling()
     }
 
-    @MainActor
-    func handleNostrMessage(_ giftWrap: NostrEvent) {
-        nostrCoordinator.inbound.handleNostrMessage(giftWrap)
-    }
-
-    func processNostrMessage(_ giftWrap: NostrEvent) async {
-        await nostrCoordinator.inbound.processNostrMessage(giftWrap)
-    }
-
     @MainActor
     func findNoiseKey(for nostrPubkey: String) -> Data? {
         nostrCoordinator.inbound.findNoiseKey(for: nostrPubkey)
     }
 
-    @MainActor
-    func sendDeliveryAckViaNostrEmbedded(
-        _ message: BitchatMessage,
-        wasReadBefore: Bool,
-        senderPubkey: String,
-        key: Data?
-    ) {
-        nostrCoordinator.sendDeliveryAckViaNostrEmbedded(
-            message,
-            wasReadBefore: wasReadBefore,
-            senderPubkey: senderPubkey,
-            key: key
-        )
-    }
-
     @MainActor
     func sendFavoriteNotificationViaNostr(noisePublicKey: Data, isFavorite: Bool) {
         nostrCoordinator.sendFavoriteNotificationViaNostr(noisePublicKey: noisePublicKey, isFavorite: isFavorite)