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/tauri.conf.json

@@ -0,0 +1,44 @@
+{
+  "$schema": "https://schema.tauri.app/config/2",
+  "productName": "Mermix",
+  "version": "0.1.0",
+  "identifier": "dev.mermix.app",
+  "build": {
+    "beforeDevCommand": "npm run dev",
+    "devUrl": "http://localhost:1420",
+    "beforeBuildCommand": "npm run build",
+    "frontendDist": "../dist"
+  },
+  "app": {
+    "windows": [
+      {
+        "title": "Mermix",
+        "width": 1280,
+        "height": 820,
+        "minWidth": 880,
+        "minHeight": 560,
+        "resizable": true,
+        "fullscreen": false,
+        "center": true
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all",
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ],
+    "category": "DeveloperTool",
+    "shortDescription": "Mermaid editor & viewer with Git-backed projects",
+    "longDescription": "Mermix is a cross-platform Mermaid diagram editor and viewer. Organize many diagrams into projects backed by Git for branches, versions and commit history."
+  },
+  "plugins": {}
+}