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/vite.config.js

@@ -0,0 +1,32 @@
+import { defineConfig } from "vite";
+import { sveltekit } from "@sveltejs/kit/vite";
+
+// @ts-expect-error process is a nodejs global
+const host = process.env.TAURI_DEV_HOST;
+
+// https://vite.dev/config/
+export default defineConfig(async () => ({
+  plugins: [sveltekit()],
+
+  // Vite options tailored for Tauri development and only applied in `tauri dev` or `tauri build`
+  //
+  // 1. prevent Vite from obscuring rust errors
+  clearScreen: false,
+  // 2. tauri expects a fixed port, fail if that port is not available
+  server: {
+    port: 1420,
+    strictPort: true,
+    host: host || false,
+    hmr: host
+      ? {
+          protocol: "ws",
+          host,
+          port: 1421,
+        }
+      : undefined,
+    watch: {
+      // 3. tell Vite to ignore watching `src-tauri`
+      ignored: ["**/src-tauri/**"],
+    },
+  },
+}));