chat: peer-switch strip, back button moved to flyout header

Switching conversations used to require bouncing back to the list view
and picking from there. Now the thread view has a horizontal peer
strip at the top: one click hops to another conversation, active tab
is highlighted and auto-scrolls into view, unread peers show a dot.
Scrollbar is hidden — vertical wheel delta is redirected to horizontal
scroll so the user can slide the strip with the mouse wheel when it
overflows.

In-thread header is gone; the back button moved next to "chat" in the
flyout header and only shows while a thread is open. Peer name stays
visible via the active tab.

Bumps to 1.9.3.

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

electron/package.json

@@ -1,6 +1,6 @@
 {
   "name": "hyprcrd",
-  "version": "1.9.2",
+  "version": "1.9.3",
   "description": "hyprcrd — self-hosted card manager",
   "main": "main.js",
   "scripts": {