docs: add workspace collaboration design and client demos

Document shared workspaces, realtime messaging, member handling, and source permissions. Include local interaction demos and verification scripts, and update development startup for Electron Node mode. Production collaboration services remain unimplemented.

package.json

@@ -4,8 +4,8 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "dev": "concurrently -k -n api,web -c cyan,magenta \"npm:dev:api\" \"npm:dev:web\"",
-    "dev:api": "tsx watch server/index.ts",
+    "dev": "node scripts/dev.mjs",
+    "dev:api": "node --watch --import tsx server/index.ts",
     "dev:web": "vite",
     "build": "npm run typecheck && vite build && npm run build:server",
     "build:server": "node -e \"require('node:fs').rmSync('build-server',{recursive:true,force:true})\" && tsc -p tsconfig.server.json",