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>

agent/MEMORY.md

@@ -7,6 +7,11 @@ here the moment a debugging session teaches you something a future
 iteration would otherwise rediscover.
 
 ## Testing & VM recipes
+- A checks.* fixture CANNOT be a writeText/toFile state file read at
+  eval time ("path … is not valid" — flake check's eval store won't
+  realise it): extract the logic into a pure importable file and
+  unit-test THAT (monitor-rules.nix / checks.display-profiles is the
+  pattern).
 - CI (`.gitea/workflows/check.yml`) is **eval-tier only**: the act_runner
   is a docker container (no systemd, no /dev/kvm). Container gotchas are
   documented in the workflow header (single-user Nix + nixbld users,