fix(install): bake dconf, seed main, name ISO, display modes (#123–#126)

Batch of existing-bug fixes from Acer/XPS install findings:

- #123: HM pre-activate creates /run/user/$UID and prefers
  dbus-run-session so dconf no longer aborts the desktop bake
- #124: main-built ISOs seed ?ref=main; patch-template rewrites
  inputs.nomarchy.url from NOMARCHY_FLAKE_URL (was set but unused)
- #125: image.baseName → nomarchy-live-….iso (not nixos-live-…)
- #126: Display mode list sorted by pixel area; toast shows hyprctl
  size; TESTING notes QEMU fixed-window scaling illusion

Verified: V0 flake check, installer-safety, baseName eval, patch-template
flakeUrl rewrite, mode-sort fixture.

README.md

@@ -110,7 +110,7 @@ Boot the full desktop from a USB stick or VM without installing anything:
 
 ```sh
 nix build .#nixosConfigurations.nomarchy-live.config.system.build.isoImage
-# → result/iso/*.iso — dd to a stick, or boot it in QEMU:
+# → result/iso/nomarchy-live-….iso — dd to a stick, or boot it in QEMU:
 tools/test-live-iso.sh
 ```