IMAPS, SMTP submission, sieve filtering, DKIM, full-text search.
Remove dead code internet-gateway.nix and hackerfleet exim router.
Add mail and DKIM dirs to borg backup.

Use `nix build --print-out-paths` + PYTHONPATH instead of `nix shell`
for the websocket-client bootstrap. Caches the store path in /tmp.
Goes from 30s+ to under 1s.

- Disable spurious PCIe wakeup sources via udev rule
- Add 64GB swapfile and resume config for hibernation
- Enable suspend-then-hibernate (15min s2idle, then hibernate)
- Load amdgpu in initrd for reliable resume
- Add amdgpu.gpu_recovery=1 kernel param
- Pre-evict VRAM before sleep via systemd service