feat(app): app icon and macOS bundle config

The dock showed a black square because tauri.conf.json had no bundle.icon
block and icons/ held only tiny placeholders with no .icns. Add an SVG
source logo (terminal prompt + split workspace panes), generate the full
icon set via `tauri icon` (icon.icns/.ico + all PNG/iOS/Android sizes), and
wire bundle.icon so the daemon embeds and macOS renders it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src-tauri/tauri.conf.json

@@ -12,5 +12,15 @@
   "app": {
     "windows": [{ "title": "spacesh", "width": 1100, "height": 720 }],
     "security": { "csp": null }
+  },
+  "bundle": {
+    "active": true,
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ]
   }
 }