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/App.test.tsx

@@ -0,0 +1,130 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import App from "./App";
+import type { Settings } from "./lib/types";
+import { useConnectionStore } from "./stores/connectionStore";
+import { useSettingsStore } from "./stores/settingsStore";
+import { useUiStore } from "./stores/uiStore";
+
+vi.mock("./lib/commands", () => ({
+  getConnections: vi.fn().mockResolvedValue([]),
+  getFolders: vi.fn().mockResolvedValue([]),
+  getTags: vi.fn().mockResolvedValue([]),
+  getSettings: vi.fn().mockResolvedValue({
+    confirm_before_delete: true,
+    default_folder_id: null,
+    theme: "dark",
+    font_size: "medium",
+    default_ports: { postgresql: 5432, mysql: 3306, redis: 6379, sqlite: null },
+    tag_order: null,
+    table_refresh_rate: 30,
+    table_page_size: 50,
+    shortcuts: {},
+    accent_color: "#2563EB",
+    editor_font_size: 13,
+    editor_font_family: "Space Mono",
+    editor_word_wrap: "off",
+    editor_minimap: false,
+    editor_tab_size: 4,
+  } satisfies Settings),
+  testConnection: vi.fn().mockResolvedValue({ ok: true }),
+}));
+
+beforeEach(() => {
+  useConnectionStore.setState({
+    connections: [],
+    folders: [],
+    tags: [],
+    loading: false,
+    error: null,
+  });
+  useSettingsStore.setState({ settings: null, loading: false, error: null });
+  useUiStore.setState({ activeView: "home" });
+  useUiStore.setState({ activeFolderId: null });
+  vi.clearAllMocks();
+});
+
+describe("App", () => {
+  it("renders home view on mount", async () => {
+    render(<App />);
+    expect(await screen.findByPlaceholderText(/search connections/i)).toBeInTheDocument();
+  });
+
+  it("shows empty state when no connections", async () => {
+    render(<App />);
+    expect(await screen.findByText(/no connections/i)).toBeInTheDocument();
+  });
+
+  it("loads data on mount", async () => {
+    render(<App />);
+    await screen.findByPlaceholderText(/search connections/i);
+    expect(useConnectionStore.getState().loading).toBe(false);
+  });
+
+  it("renders settings page when activeView is settings", async () => {
+    useUiStore.setState({ activeView: "settings" });
+    render(<App />);
+    expect(screen.getByRole("heading", { name: /general/i })).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: /back/i })).toBeInTheDocument();
+  });
+
+  it("renders new connection form when activeView is new-connection", async () => {
+    useUiStore.setState({ activeView: "new-connection" });
+    render(<App />);
+    expect(await screen.findByText("Save Connection")).toBeInTheDocument();
+  });
+
+  it("shows error banner when connectionStore has error", async () => {
+    const { getConnections } = await import("./lib/commands");
+    vi.mocked(getConnections).mockRejectedValueOnce(new Error("Storage error"));
+    useConnectionStore.setState({ connections: [], loading: false, error: null });
+    render(<App />);
+    expect(await screen.findByText(/storage error/i)).toBeInTheDocument();
+  });
+
+  it("sets the active folder from default_folder_id on startup", async () => {
+    const { getFolders, getSettings } = await import("./lib/commands");
+    vi.mocked(getFolders).mockResolvedValueOnce([
+      {
+        id: "folder-1",
+        name: "Projects",
+        parent_id: null,
+        tag_ids: [],
+        created_at: "",
+        updated_at: "",
+      },
+    ]);
+    // Resolve settings only after folders have loaded so the default-folder
+    // effect doesn't race HomeScreen's "reset missing folder" effect.
+    let resolveSettings!: (value: Settings) => void;
+    vi.mocked(getSettings).mockImplementationOnce(
+      () =>
+        new Promise<Settings>((resolve) => {
+          resolveSettings = resolve;
+        }),
+    );
+    useUiStore.setState({ activeFolderId: null });
+    render(<App />);
+    await screen.findByPlaceholderText(/search connections/i);
+    resolveSettings({
+      confirm_before_delete: true,
+      default_folder_id: "folder-1",
+      theme: "dark",
+      font_size: "medium",
+      default_ports: { postgresql: 5432, mysql: 3306, redis: 6379, sqlite: null },
+      tag_order: null,
+      table_refresh_rate: 30,
+      table_page_size: 50,
+      shortcuts: {},
+      accent_color: "#2563EB",
+      editor_font_size: 13,
+      editor_font_family: "Space Mono",
+      editor_word_wrap: "off",
+      editor_minimap: false,
+      editor_tab_size: 4,
+    });
+    await waitFor(() => {
+      expect(useUiStore.getState().activeFolderId).toBe("folder-1");
+    });
+  });
+});