chore: scaffold Tauri 2 + Svelte 5 workspace

Standard Tauri layout with a Svelte 5 + TypeScript + Vite frontend and a
Rust backend in src-tauri. Adds build tooling, app/window config,
capabilities, generated icons and the project README.

src-tauri/capabilities/default.json

@@ -0,0 +1,16 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "Default permissions for the Mermix main window",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    "core:window:allow-start-dragging",
+    "core:window:allow-set-title",
+    "dialog:default",
+    "dialog:allow-open",
+    "dialog:allow-save",
+    "dialog:allow-message",
+    "dialog:allow-ask"
+  ]
+}