Replace custom setup wizard with Database Manager (like Python Odoo)

Flow now mirrors Python Odoo exactly:
1. Empty DB → /web redirects to /web/database/manager
2. User fills: master_pwd, email (login), password, phone, lang, country, demo
3. Backend creates admin user, company, seeds chart of accounts
4. Auto-login → redirect to /odoo (webclient)

Removed:
- Custom /web/setup wizard
- Auto-seed on startup

Added:
- /web/database/manager (mirrors odoo/addons/web/controllers/database.py)
- /web/database/create (mirrors exp_create_database)
- Auto-login after DB creation with session cookie

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pkg/server/webclient.go

@@ -66,9 +66,10 @@ func loadAssetList(name string, fs embed.FS) []string {
 // handleWebClient serves the Odoo webclient HTML shell.
 // Mirrors: odoo/addons/web/controllers/home.py Home.web_client()
 func (s *Server) handleWebClient(w http.ResponseWriter, r *http.Request) {
-	// Check if setup is needed
+	// Check if database needs initialization
+	// Mirrors: odoo/addons/web/controllers/home.py ensure_db()
 	if s.isSetupNeeded() {
-		http.Redirect(w, r, "/web/setup", http.StatusFound)
+		http.Redirect(w, r, "/web/database/manager", http.StatusFound)
 		return
 	}