feat(displays): hotplug auto-switch for display profiles (item 15b)

nomarchy-display-profile gains `match <outputs>`: an exact set match
wins, else the largest profile whose named outputs are all connected;
any tie prints nothing — the watcher must never flap between ambiguous
layouts. nomarchy-display-profile-watch (exec-once when profiles are
declared, the keyboard-watcher poll pattern — session units race
Hyprland IPC on relogin) reacts to output-set CHANGES only, reads
settings.displayProfileAuto from the live state each time (the menu's
new Auto-switch row toggles it instantly, no rebuild), and applies via
the tool — so an auto-pick persists a concrete profile that the next
rebuild bakes. A separate boolean rather than an "auto" pseudo-profile
for exactly that bake semantics.

Verified: V0 (flake check); V1 — a scratch 4-profile downstream builds;
tool + watcher pass bash -n; the match matrix exercised end-to-end:
three exact picks, an unambiguous-superset pick, a tie -> none, a
no-fit -> none; the watcher is exec-once'd in the rendered config; the
menu renders the Auto-switch row. Remains: V3 real dock/undock
(HARDWARE-QUEUE, rides the slice-a entry). Slice c (workspace binding)
stays, tagged optional.

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

modules/home/rofi.nix

@@ -394,11 +394,26 @@ ${themeRows}
             if [ "$p" = "$active" ]; then printf '● %s\n' "$p"; else printf '○ %s\n' "$p"; fi
           done
           printf 'Base layout\n'
+          if [ "$(nomarchy-theme-sync get settings.displayProfileAuto 2>/dev/null)" = true ]
+          then printf 'Auto-switch (on)\n'
+          else printf 'Auto-switch (off)\n'
+          fi
           printf '%s\n' "$BACK"
         } | rofi -dmenu -p Profiles ) || exit 0
         case "$choice" in
           "$BACK")        exec "$0" display ;;
           "Base layout")  exec nomarchy-display-profile base ;;
+          *"Auto-switch"*)
+            # Instant in-flake flag; the watcher reads it live on the next
+            # output change — no rebuild, no unit juggling.
+            if [ "$(nomarchy-theme-sync get settings.displayProfileAuto 2>/dev/null)" = true ]; then
+              nomarchy-theme-sync --quiet set settings.displayProfileAuto false --no-switch
+              notify-send "Display profiles" "Auto-switch off — profiles change only from this menu."
+            else
+              nomarchy-theme-sync --quiet set settings.displayProfileAuto true --no-switch
+              notify-send "Display profiles" "Auto-switch on — plugging/unplugging outputs picks the matching profile."
+            fi
+            exec "$0" display-profile ;;
           *)              exec nomarchy-display-profile apply "''${choice#[●○] }" ;;
         esac ;;