feat(displays): display profiles — docked/undocked switching (item 15a)

nomarchy.displayProfiles: named layouts for the same outputs, each a
list of nomarchy.monitors-style entries. The active profile lives in
the in-flake state (settings.displayProfile) on the night-light
pattern: nomarchy-display-profile apply <name> fires the baked hyprctl
rules instantly and writes the state with --no-switch; the next rebuild
bakes the profile's entries over nomarchy.monitors whole-by-name.
Monitor-rule composition is extracted to pure monitor-rules.nix
(renderer + 3-layer resolve, incl. a disable-guard so a stale menu
resolution pick can't resurrect a profile-disabled panel, and junk
state degrading to base config instead of an eval error) — because a
writeText/toFile state fixture is unreadable at flake-check eval time,
the new checks.display-profiles unit-tests the pure function directly.
Menu: System › Display gains a self-gated "Profiles ›" row (●/○ active
mark, Base layout to clear); commented template example + README row.

Verified: V0 (flake check, forcing the new check's asserts); V1 — a
scratch downstream through lib.mkFlake builds: the generated tool
passes bash -n with correct rules (disable/vrr/float scale), the baked
hyprland.conf shows the exact expected overlay, the menu renders, and
list/usage smoke-test clean. Remains: V3 live switching on a dock
(HARDWARE-QUEUE). Slices b (hotplug auto-switch) + c (workspace
binding) stay in item 15.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

templates/downstream/home.nix

@@ -34,6 +34,16 @@
   #   { name = "HDMI-A-1"; position = "auto-right"; }
   # ];                                  #   names from `hyprctl devices`
   #
+  # nomarchy.displayProfiles = {        # named layouts for the SAME outputs —
+  #   docked = [                        #   switch: System › Display › Profiles
+  #     { name = "eDP-1"; resolution = "disable"; }
+  #     { name = "DP-3"; position = "0x0"; }
+  #     { name = "DP-4"; position = "auto-right"; }
+  #   ];
+  #   undocked = [ { name = "eDP-1"; position = "0x0"; } ];
+  # };                                  #   applied instantly + remembered in the
+  #                                     #   flake state (settings.displayProfile)
+  #
   # nomarchy.keyboard.devices = {       # a specific keyboard's own layout
   #   "keychron-keychron-k2" = { layout = "de"; };
   # };