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/lib/bundle-config.test.ts

@@ -0,0 +1,11 @@
+import { describe, it, expect } from "vitest";
+import tauriConf from "../../src-tauri/tauri.conf.json";
+
+describe("tauri bundle config (v0.7.10)", () => {
+  it("declares bundled pg_tools resources", () => {
+    expect(tauriConf.bundle.resources).toContain("resources/pg_tools/*");
+  });
+  it("version is 0.7.10", () => {
+    expect(tauriConf.version).toBe("0.7.10");
+  });
+});