relay: file attachments, outbox, CC-self, chat view, mobile layout

Compose: attach files (encrypted, hex-named, linked via relay_uid),
CC-self checkbox tags copy with recipient name. Outbox section shows
sent messages with delete. Chat view: session-based threads/history/
send endpoints, split layout with sidebar, read receipts, 5s poll.
Mobile: threads as horizontal scroll bar above messages. Fix chat
input pushed offscreen by adding min-height:0 on flex container.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

electron/package.json

@@ -1,6 +1,6 @@
 {
   "name": "hyprcrd",
-  "version": "1.3.4",
+  "version": "1.3.5",
   "description": "hyprcrd — self-hosted card manager",
   "main": "main.js",
   "scripts": {