fix(linux): launch on NVIDIA + Wayland; config webAppUrl for "call in browser"

NVIDIA + Wayland (reported on CachyOS/KDE, driver 615.71, webkit2gtk
2.52.6): no window. GDK dies with "Error 71 (Protocol error) dispatching to
Wayland display"; forced onto XWayland, WebKit's DMA-BUF renderer then fails
with "Failed to create GBM buffer … Invalid argument". The reporter's
workaround, WEBKIT_DISABLE_DMABUF_RENDERER=1 GDK_BACKEND=x11, runs fine.

gpu_workarounds::apply(), first thing in main() (before GTK/WebKit init):
when the NVIDIA driver is loaded (/proc/driver/nvidia/version or
/sys/module/nvidia), set WEBKIT_DISABLE_DMABUF_RENDERER=1, and on a Wayland
session that has XWayland (DISPLAY set) also GDK_BACKEND=x11. Values the user
already set win; LOTUS_NO_GPU_WORKAROUNDS=1 turns it all off. Logs what it
set to stderr. Non-NVIDIA systems are untouched. Unit tests for the decision.

config.json: webAppUrl = https://chat.lotusguild.org, used by the web client
(cinny `calls-open-in-browser`) to send calls this WebKitGTK build can't make
to the web app in the browser.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

config.json

@@ -8,13 +8,21 @@
   "allowCustomHomeservers": true,
   "featuredCommunities": {
     "openAsDefault": false,
-    "spaces": ["!-1ZBnAH-JiCOV8MGSKN77zDGTuI3pgSdy8Unu_DrDyc", "#homelab:codestorm.net"],
-    "rooms": ["#jellyfin:matrix.org"],
-    "servers": ["matrixrooms.info"]
+    "spaces": [
+      "!-1ZBnAH-JiCOV8MGSKN77zDGTuI3pgSdy8Unu_DrDyc",
+      "#homelab:codestorm.net"
+    ],
+    "rooms": [
+      "#jellyfin:matrix.org"
+    ],
+    "servers": [
+      "matrixrooms.info"
+    ]
   },
   "hashRouter": {
     "enabled": true,
     "basename": "/"
   },
-  "gifApiKey": ""
-}
+  "gifApiKey": "",
+  "webAppUrl": "https://chat.lotusguild.org"
+}