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/connections/ProviderSetupGuide.tsx

@@ -0,0 +1,50 @@
+import { useState } from "react";
+import { ChevronDown } from "lucide-react";
+import { SETUP_GUIDES } from "../../lib/providers";
+
+interface ProviderSetupGuideProps {
+  provider: "supabase" | "neon";
+}
+
+const SSL_NOTE: Record<"supabase" | "neon", string> = {
+  supabase: "SSL is required by Supabase.",
+  neon: "Neon requires SSL.",
+};
+
+export function ProviderSetupGuide({ provider }: ProviderSetupGuideProps) {
+  const [open, setOpen] = useState(false);
+  const guide = SETUP_GUIDES[provider];
+
+  return (
+    <div className="mt-2 border border-border rounded-lg bg-surface">
+      <button
+        type="button"
+        onClick={() => setOpen((o) => !o)}
+        aria-label="How to connect"
+        className="w-full flex items-center justify-between px-3 py-2 text-xs text-text-muted hover:text-text cursor-pointer transition-colors"
+      >
+        <span>How to connect</span>
+        <ChevronDown
+          size={14}
+          className={open ? "rotate-180 transition-transform" : "transition-transform"}
+          aria-hidden="true"
+        />
+      </button>
+
+      {guide.sslRequired && (
+        <p className="px-3 pb-2 text-xs text-accent-muted">{SSL_NOTE[provider]}</p>
+      )}
+
+      {open && (
+        <ol className="px-3 pb-3 space-y-2 list-decimal list-inside text-xs text-text-muted">
+          {guide.steps.map((step, i) => (
+            <li key={i} className="space-y-0.5">
+              <span className="text-text font-medium">{step.title}</span>
+              <p className="text-text-muted">{step.detail}</p>
+            </li>
+          ))}
+        </ol>
+      )}
+    </div>
+  );
+}