feat: scaffold Tauri + Svelte client

SvelteKit in SPA mode with Tauri v2. Builds and produces .deb bundle.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/src-tauri/capabilities/default.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "Capability for the main window",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    "opener:default"
+  ]
+}