Verify Nostr inbound signatures once, off the main actor

Every inbound relay event was Schnorr-verified TWICE, both times on the
main actor: once in NostrRelayManager.handleParsedMessage and again in
each NostrInboundPipeline / GeoPresenceTracker handler. Each
verification re-serializes the event JSON, hashes it, and runs a
secp256k1 Schnorr verify, so busy geohashes paid double crypto on the
UI thread. Geohash gift-wrap NIP-17 decryption (two ECDH+ChaCha layers)
also ran on the main actor.

Changes:
- NostrRelayManager now owns a serial off-main inbound pipeline
  (AsyncStream + single consumer task): frames are parsed and verified
  in arrival order off the main actor, preserving per-subscription
  delivery order. This is the single verification point for the whole
  inbound path; downstream handlers only ever see verified events.
- Dedup stays two-phase and unpoisonable: a cheap main-actor duplicate
  LOOKUP runs before verification (duplicate fan-in from several relays
  never pays for crypto — previously every duplicate was verified), and
  events are RECORDED as seen only after the signature verifies, so a
  forged-signature copy can never suppress the genuine event.
- NostrInboundPipeline and GeoPresenceTracker drop their redundant
  re-verification; geohash gift-wrap decryption moves off the main
  actor following the existing account-mailbox Task.detached pattern
  (atomic main-actor check-and-record, then decrypt off-main, then hop
  back for state updates).
- Tests: relay-level coverage for tampered gift wraps and for in-order
  delivery of back-to-back frames; pipeline-level tampered-signature
  tests move to the relay boundary where the invariant now lives; the
  mock relay connection queues frames emitted before receive re-arms.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bitchatTests/Performance/PerformanceBaselineTests.swift

@@ -77,8 +77,10 @@ final class PerformanceBaselineTests: XCTestCase {
     // MARK: - 1a. Nostr inbound event handling (fresh events)
 
     /// `NostrInboundPipeline.handleNostrEvent` for never-seen geo events
-    /// (kind 20000): signature verification, dedup record, presence/nickname
-    /// bookkeeping, and public-message ingest scheduling.
+    /// (kind 20000): dedup record, presence/nickname bookkeeping, and
+    /// public-message ingest scheduling. Schnorr signature verification is
+    /// NOT part of this path anymore — it runs exactly once, off the main
+    /// actor, in `NostrRelayManager` before delivery.
     func testNostrInboundEventHandling_freshEvents() throws {
         let events = try Self.makeSignedGeohashEvents(count: 500)
         // A fresh context per measure pass so every event takes the
@@ -106,8 +108,9 @@ final class PerformanceBaselineTests: XCTestCase {
 
     /// The dedup-hit path: identical events replayed. Duplicates dominate
     /// real relay traffic (the same event arrives from several relays), so
-    /// this path runs hundreds of times a minute in busy geohashes. Note it
-    /// still pays full Schnorr signature verification before the dedup check.
+    /// this path runs hundreds of times a minute in busy geohashes. It is a
+    /// pure dedup lookup: no crypto (verification happens upstream in
+    /// `NostrRelayManager`, and only for the first-seen copy).
     func testNostrInboundEventHandling_duplicateEvents() throws {
         let events = try Self.makeSignedGeohashEvents(count: 500)
         let context = PerfNostrContext()