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/Utils/MessageDeduplicator.swift

@@ -52,18 +52,6 @@ final class MessageDeduplicator {
         return false
     }
 
-    /// Record an ID with a specific timestamp (for content key tracking)
-    func record(_ id: String, timestamp: Date) {
-        lock.lock()
-        defer { lock.unlock() }
-
-        if lookup[id] == nil {
-            entries.append(Entry(id: id, timestamp: timestamp))
-        }
-        lookup[id] = timestamp
-        trimIfNeeded()
-    }
-
     /// Add an ID without checking (for announce-back tracking)
     func markProcessed(_ id: String) {
         lock.lock()
@@ -83,13 +71,6 @@ final class MessageDeduplicator {
         return lookup[id] != nil
     }
 
-    /// Get timestamp for an ID (for content deduplication time-window checks)
-    func timestampFor(_ id: String) -> Date? {
-        lock.lock()
-        defer { lock.unlock() }
-        return lookup[id]
-    }
-
     private func trimIfNeeded() {
         let activeCount = entries.count - head
         guard activeCount > maxCount else { return }

bitchat/Utils/Theme.swift

@@ -96,7 +96,7 @@ struct ThemePalette {
         )
     }
 
-    static func liquidGlass(_ colorScheme: ColorScheme) -> ThemePalette {
+    static func liquidGlass(_: ColorScheme) -> ThemePalette {
         ThemePalette(
             background: systemBackground,
             primary: .primary,