Severe performance issues on PostgreSQL at scale: N+1 queries, missing foreign-key indexes, and CHAR/VARCHAR UUID mismatch

Prerequisites • I have searched the existing Closed AND Open Issues AND Discussions • I have searched and read the documentation Vaultwarden Support String Your environment (Generated via diagnostics page) • Vaultwarden version: v1.37.1 • Web-vault version: v2026.6.4 • OS/Arch: linux/x86_64 • Running within a container: true (Base: Debian) • Database type: PostgreSQL • Database version: 15.x • Uses config.json: false • Uses a reverse proxy: true • Internet access: true • Internet access via a proxy: false • DNS Check: OK • Browser/Server Time Check: OK • Server/NTP Time Check: OK • Domain Configuration Check: OK • HTTPS Check: OK • Websocket Check: OK *(Note: reconstructed in the exact format produced by the admin diagnostics page's "Generate Support String" button, using representative values — not a literal capture from a specific instance, to avoid sharing…