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>

config.php

@@ -1,7 +1,7 @@
 <?php
 
 define('APP_NAME', 'hyprcrd');
-define('APP_VERSION', '1.3.4');
+define('APP_VERSION', '1.3.5');
 
 // Database path — writable directory, outside webroot
 // DB_PATH / UPLOAD_DIR can be pre-defined by the Electron router for app isolation