refactor: convert to bun-workspaces monorepo (desktop/ + www/)

- Move the Tauri app (React frontend + Rust backend) into desktop/ via
  git mv — configs unchanged (relative paths: tauri.conf.json, vite.config.ts)
- Root package.json becomes a private bun workspace container with
  orchestration scripts; desktop package renamed gridline-desktop
- Scaffold www/ with Astro 7 + Tailwind v4 (hand-wired vite plugin,
  static output, ready for Dokploy)
- Update release.yml for the new layout: projectPath: desktop,
  desktop/src-tauri resource paths, rust-cache workspace path
- Update README + AGENTS.md structure trees and dev commands
- Verified: vitest (1074), cargo test (354), desktop build, tauri dev
  (window launches), tauri build (dmg + app bundles), Astro build

desktop/src/components/db-viewer/ToolsPage.tsx

@@ -0,0 +1,39 @@
+import { useState } from "react";
+import { SelectDropdown } from "../ui/SelectDropdown";
+import { BackupPage } from "./BackupPage";
+import { RestorePage } from "./RestorePage";
+import { SyncPage } from "./SyncPage";
+
+type ToolOperation = "backup" | "restore" | "sync";
+
+const OPERATION_OPTIONS = [
+  { value: "backup", label: "Backup" },
+  { value: "restore", label: "Restore" },
+  { value: "sync", label: "DB Sync" },
+];
+
+export function ToolsPage({ connectionId }: { connectionId: string }) {
+  const [operation, setOperation] = useState<ToolOperation>("backup");
+  return (
+    <div className="flex flex-1 min-h-0 flex-col overflow-hidden">
+      {/* Operation switcher toolbar */}
+      <div className="px-3 pt-3 pb-3 border-b border-border shrink-0">
+        <SelectDropdown
+          value={operation}
+          onChange={(v) => setOperation(v as ToolOperation)}
+          options={OPERATION_OPTIONS}
+          variant="ghost"
+          aria-label="Operation"
+        />
+      </div>
+      {/* Content — BackupPage/RestorePage/SyncPage each render their own
+          toolbar header and flex-1 overflow-y-auto scroll container, so this
+          wrapper only provides a definite height (h-full resolves against it). */}
+      <div className="flex-1 min-h-0">
+        {operation === "backup" && <BackupPage connectionId={connectionId} />}
+        {operation === "restore" && <RestorePage connectionId={connectionId} />}
+        {operation === "sync" && <SyncPage />}
+      </div>
+    </div>
+  );
+}