Group authors, avatars everywhere, QR scan/share, and iOS-parity Messages bar

- Session.Line carries `author` (record always persisted it; the read
  side never surfaced it) — group bubbles now wear the WRITER's name and
  picture instead of the group's initial for every message.
- Story cards use the author's real picture (your own from myAvatar).
- avatarShared marker stamps the peer's device set, not just the blob
  id: a bare marker outlived their reinstall and they saw initials for
  ever. Old markers mismatch once and self-heal with one resend.
- QR: AddressCard embeds ?u=<handle> so a same-relay scan resolves
  through the ordinary username lookup, and the Home + Messages bars
  gain a scanner — WebRTC's own Camera2 capture rendered to a
  SurfaceViewRenderer with each frame's Y plane offered to zxing:core
  (the one new dependency; decode only, no second camera framework).
  parseScannedAddress mirrors iOS ContactCard.decode's refusals.
- Messages screen matches iOS: bare title with scan + add-contact
  actions, New group beside the Groups heading (GroupsSection's own
  label, always drawn now, carries it), New chat beside CHATS with a
  contact picker, and the duplicated GROUPS label is gone.
- Story composer gains a per-story audience: Everyone / Only… /
  All except… chips with a member checklist, seeded from the account
  setting, never written back to it. postStory takes the override.
- AddContactForm accepts a prefill so a scan lands in the field —
  looked up, then added, never auto-added.

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

client/src/main/kotlin/io/flamenet/client/Conversations.kt

@@ -309,9 +309,20 @@ class Conversations(
      */
     fun shareAvatarIfNeeded(toUserId: Long) {
         val ref = vault.myAvatar() ?: return
-        if (vault.avatarSharedWith(toUserId) == ref.id) return
+        // 🔴 The marker records WHICH DEVICES were told, not just which
+        // picture. A bare ref.id marker outlived the peer's reinstall: their
+        // new install held no avatar, this side said "already shared", and
+        // they saw initials for ever — the same staleness class as the
+        // delivery key. The directory endpoint is free (no prekey popped).
+        val devices = runCatching { relay.listDevices(toUserId) }.getOrNull() ?: return
+        val ids = (0 until devices.length())
+            .map { devices.getJSONObject(it).optString("device_id") }
+            .sorted().joinToString(",")
+        if (ids.isEmpty()) return
+        val stamp = "${ref.id}|$ids"
+        if (vault.avatarSharedWith(toUserId) == stamp) return
         runCatching { sendPlaintext(toUserId, Content.avatar(ref)) }
-            .onSuccess { vault.markAvatarShared(toUserId, ref.id) }
+            .onSuccess { vault.markAvatarShared(toUserId, stamp) }
     }
 
     /**