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-tauri/tauri.conf.json

@@ -0,0 +1,44 @@
+{
+  "$schema": "https://schema.tauri.app/config/2",
+  "productName": "Gridline",
+  "version": "0.7.10",
+  "identifier": "com.adrianbonpin.gridline",
+  "build": {
+    "beforeDevCommand": "bun run dev",
+    "devUrl": "http://localhost:1420",
+    "beforeBuildCommand": "bun run build",
+    "frontendDist": "../dist"
+  },
+  "app": {
+    "windows": [
+      {
+        "title": "Gridline",
+        "width": 1200,
+        "height": 800,
+        "backgroundColor": "#0A0A0B",
+        "titleBarStyle": "Overlay"
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all",
+    "resources": ["resources/pg_tools/*", "resources/mysql_tools/*"],
+    "macOS": {
+      "signingIdentity": "-",
+      "hardenedRuntime": false
+    },
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ]
+  },
+  "plugins": {}
+}