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/Cargo.toml

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+[package]
+name = "mermix"
+version = "0.1.0"
+description = "Cross-platform Mermaid editor & viewer with Git-backed projects"
+authors = ["Mermix"]
+edition = "2021"
+rust-version = "1.77"
+
+[lib]
+# The `_lib` suffix keeps the library name distinct from the binary so the
+# Tauri mobile bindings can link against it.
+name = "mermix_lib"
+crate-type = ["staticlib", "cdylib", "rlib"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = [] }
+tauri-plugin-dialog = "2"
+
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+
+# App-level metadata store (project registry + settings).
+sqlx = { version = "0.8", default-features = false, features = [
+    "runtime-tokio",
+    "sqlite",
+    "chrono",
+    "macros",
+] }
+
+# Per-project version control.
+git2 = "0.19"
+
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "fs", "sync"] }
+thiserror = "1"
+chrono = { version = "0.4", features = ["serde"] }
+uuid = { version = "1", features = ["v4", "serde"] }
+directories = "5"
+toml = "0.8"
+
+[features]
+# This feature is used for production builds or when a dev server is not
+# specified, DO NOT REMOVE!!
+custom-protocol = ["tauri/custom-protocol"]
+
+[profile.release]
+panic = "abort"
+codegen-units = 1
+lto = true
+opt-level = "s"
+strip = true

src-tauri/build.rs

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+fn main() {
+    tauri_build::build()
+}

src-tauri/capabilities/default.json

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+{
+  "$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"
+  ]
+}

src-tauri/icons/android/mipmap-anydpi-v26/ic_launcher.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+  <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
+  <background android:drawable="@color/ic_launcher_background"/>
+</adaptive-icon>

src-tauri/icons/android/values/ic_launcher_background.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+  <color name="ic_launcher_background">#fff</color>
+</resources>

src-tauri/tauri.conf.json

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+{
+  "$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": {}
+}