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>

README.md

@@ -228,6 +228,7 @@ two tables below are split along exactly that line.
 | `nomarchy.viewers.enable` | `true` | Document/image viewers: zathura (Stylix-themed PDF) + imv |
 | `nomarchy.mime.enable` | `true` | Default "open with" associations (PDF/image/video/text/browser/directory); entries for apps you removed are skipped, so it degrades with the suite |
 | `nomarchy.monitors` | `[]` | Declarative per-output layout → Hyprland `monitor` rules (applied on hotplug); `,preferred,auto,1` wildcard kept as fallback |
+| `nomarchy.displayProfiles` | `{}` | Named layouts for the same outputs (docked/undocked/…), switched from System › Display › Profiles: instant via hyprctl, persisted in-flake (`settings.displayProfile`), baked over `nomarchy.monitors` at the next rebuild |
 | `nomarchy.themesDir` | Nomarchy's `themes/` | Where per-theme app overrides are probed |
 | `nomarchy.package` | overlay's `nomarchy-theme-sync` | The theme/state tool package, overridable if you fork it |