Migrate bos-settings from GTK4 to Tauri + Svelte 5

Ports every remaining view (Keybinds, the last one — dual Flat/MultiLayout
schema detection, per-action dedicated fields with a raw-JSON fallback for
anything not modeled) and removes the now-fully-dead GTK4 crate (root
Cargo.toml + src/), leaving src-tauri/ as the single Rust binary crate.

Also folds in the UX pass done alongside the migration: responsive
multi-column layout instead of a single centered column, chip/dropdown
pickers replacing free-typed fields (Wi-Fi networks, Bar style, keyboard
layout, tag lists), consistent pill-switch toggles and boxed-list card
styling across every page, and a sidebar scroll-chaining fix.

frontend/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "bos-settings-frontend",
+  "version": "0.8.0",
+  "description": "Frontend for BOS Settings",
+  "type": "module",
+  "scripts": {
+    "dev": "vite dev",
+    "build": "vite build",
+    "preview": "vite preview",
+    "check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
+    "check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
+    "tauri": "tauri"
+  },
+  "license": "MIT",
+  "dependencies": {
+    "@lucide/svelte": "^1.25.0",
+    "@tauri-apps/api": "^2",
+    "@tauri-apps/plugin-dialog": "^2.7.2",
+    "@tauri-apps/plugin-opener": "^2"
+  },
+  "devDependencies": {
+    "@sveltejs/adapter-static": "^3.0.6",
+    "@sveltejs/kit": "^2.9.0",
+    "@sveltejs/vite-plugin-svelte": "^5.0.0",
+    "@tauri-apps/cli": "^2",
+    "svelte": "^5.0.0",
+    "svelte-check": "^4.0.0",
+    "typescript": "~5.6.2",
+    "vite": "^6.0.3"
+  }
+}