feat(display): menu-driven per-output resolution, in-flake

Phase 3 of the in-flake-state philosophy (mirroring night-light + the
keyboard-layout watcher): a System ▸ Display menu item picks an output's
resolution and persists it into the flake instead of a runtime-only tweak.

- rofi.nix: the `display` case reads `hyprctl monitors -j` (auto-skips the
  chooser with one output), lists the output's advertised modes (rounded
  refresh, deduped, highest-first) plus the preferred/highres/highrr
  tokens, applies the pick INSTANTLY via `hyprctl keyword monitor` —
  keeping the output's current position + scale, so only the resolution
  changes — then persists it with `nomarchy-theme-sync set
  settings.monitors.<name> <mode> --no-switch` (no rebuild).
- theme.nix: seed `settings.monitors = {}` (output-name -> "WxH@R") so a
  sparse/older state file still evaluates; exposed via nomarchy.settings.
- hyprland.nix: `resolvedMonitors` overlays settings.monitors onto
  nomarchy.monitors by name — a declared output keeps its other fields
  with only the resolution swapped, an undeclared output (wildcard-only,
  e.g. the laptop panel) becomes a fresh rule. So a later rebuild bakes
  the menu pick into the generated monitor rule — the monitor twin of the
  keyboard graduation. The menu pick wins over a hand-set resolution (it's
  the explicit live action).

Monitor connector names are dot-free, so a direct dotted set-path is safe
(no whole-map read-modify-write like the keyboard watcher needs).

VM-verified via a headless-Hyprland nixosTest (run + removed; too heavy
for a CI gate): the graduation baked the rule into the generated
hyprland.conf, the set/get round-trip persisted, and `hyprctl keyword
monitor` actually changed the reported resolution. Only the interactive
rofi picker isn't headlessly driveable (same caveat as the keyboard watcher).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/theme.nix

@@ -61,11 +61,15 @@ let
     # settings.keyboard.devices: per-device layouts the new-keyboard watcher
     # remembers (device-name -> XKB layout), git-tracked instead of
     # ~/.local/state; they graduate into nomarchy.keyboard.devices on the next
-    # rebuild. Defaulted so a sparse/older state file still evaluates;
-    # nomarchy.settings exposes them.
+    # rebuild. settings.monitors: per-output resolutions the Display menu
+    # remembers (output-name -> "WxH@R"), overlaid onto nomarchy.monitors by
+    # name in hyprland.nix — the monitor twin of the keyboard graduation.
+    # Defaulted so a sparse/older state file still evaluates; nomarchy.settings
+    # exposes them.
     settings = {
       nightlight = { installed = false; on = true; };
       keyboard.devices = { };
+      monitors = { };
       # Automatic timezone detection (nomarchy.system.autoTimezone): a system
       # service, but the flag lives here so both sides read one source — the
       # home side gates the Waybar-refresh watcher (timezone.nix) on it.