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.

agent/MEMORY.md

@@ -137,6 +137,19 @@ iteration would otherwise rediscover.
   without a hierarchy pass.
 
 ## Gotchas (cost a debugging session once)
+- **Installer HM pre-activate needs XDG_RUNTIME_DIR (+ session bus) (#123):**
+  `runuser … activate` inside `nixos-enter` has no user session. Without
+  `mkdir -p /run/user/$UID` owned by the install user and
+  `XDG_RUNTIME_DIR` (prefer `dbus-run-session -- activate`), dconf dies
+  with Permission denied and the bake aborts mid-way — first boot looks
+  unthemed / missing nm-applet even though the system installed.
+- **ISO filename is `image.baseName` (#125):** volumeID alone does not rename
+  `result/iso/…`; force `image.baseName` to `nomarchy-…` or the artifact
+  stays `nixos-live-….iso`.
+- **Install flake ref must match the ISO branch (#124):** while `v1` lags
+  `main`, seed `?ref=main` (and compose-lock original) from main-built ISOs;
+  `NOMARCHY_FLAKE_URL` must actually rewrite `inputs.nomarchy.url` (was set
+  but unused until #124).
 - Gum `filter` returns unmatched typed text by default; catalog-only pickers
   require `--strict` plus an independent exact-membership validation boundary.
 - Waybar `layer: top` renders above **even real-fullscreen windows** — the