feat: rebrand desktop app with McpMux terracotta identity

Replace cyan/teal color scheme with terracotta brand palette, regenerate
all app icons from Neural Router branding SVG (with simplified bold M
design for small taskbar/tray sizes), add custom frameless title bar
with branded wordmark and window controls, and update all hardcoded
color references across the UI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

apps/desktop/public/mcpmux.svg

@@ -5,6 +5,15 @@
   "windows": ["main"],
   "permissions": [
     "core:default",
+    "core:window:allow-minimize",
+    "core:window:allow-maximize",
+    "core:window:allow-toggle-maximize",
+    "core:window:allow-unmaximize",
+    "core:window:allow-close",
+    "core:window:allow-is-maximized",
+    "core:window:allow-start-dragging",
+    "core:window:allow-show",
+    "core:window:allow-set-focus",
     "opener:default",
     "deep-link:default",
     "updater:default"