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/BACKLOG.md

@@ -68,9 +68,10 @@ the *same* outputs. **Plan (designed 2026-07-05, iteration #27):**
   `hyprctl keyword monitor <rule>` per entry (rules baked into the
   dispatcher at build, like everything else in rofi.nix) + state write
   + toast. Outputs the profile doesn't name keep their base rules.
-- **Slices:** (a) option + overlay + menu picker + template example
-  (opt-in ⇒ commented `templates/downstream/home.nix` block) — V1 +
-  a checks.* grep of the rendered hyprland conf, V3 real dock; (b)
+- **Slices:** (a) ✓ shipped 2026-07-05 (iteration #28): option +
+  overlay (pure `modules/home/monitor-rules.nix`, unit-tested by
+  checks.display-profiles) + `nomarchy-display-profile` applier + menu
+  Profiles row + template example — V3 (real dock) queued; (b)
   opt-in hotplug auto-switch: a socket2 watcher on monitoradded/
   removed picks the profile whose named-output set matches connected
   outputs (exact match, else largest subset, ties = no switch) —