feat(waybar): open a calendar (calcurse) on the clock click

Item 42, de-scoped by Bernardo to app-only — no account sync (the user
configures that themselves locally). Clicking the Waybar date/clock now
runs nomarchy-calendar → calcurse in a floating, centered ghostty window
tagged --class=com.nomarchy.calendar (+ --gtk-single-instance=false for a
fresh standalone window), matched by a float+size+center windowrule. The
launcher self-gates on calcurse. Dropped the clock's format-alt date
toggle (conflicts with on-click) and moved the long date into the tooltip.
Parity: on-click added to all four whole-swap jsoncs.

Ships calcurse + pwvucontrol uncommented in the downstream template
(opt-out). Enforces ghostty always installed (ghostty.nix: enable = true
unconditional; nomarchy.ghostty.enable now gates only the theming/config)
so the --class launcher can rely on it.

Verified: V0 green; four jsoncs valid JSON; V1 HM built — launcher ships,
generated clock renders on-click=nomarchy-calendar (format-alt gone, date
in tooltip), hyprland has the 3 calendar windowrules, ghostty in the HM
profile. Click→float→calcurse month view is V3 (queued). Sync is
deliberately the user's own config, not a distro feature.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/waybar.nix

@@ -82,6 +82,22 @@ let
     [ -n "$next" ] && powerprofilesctl set "$next"
   '';
 
+  # Opens calcurse (a lightweight TUI calendar, month view by default) in a
+  # floating, centered ghostty window — bound to the Waybar clock's on-click.
+  # A distinct --class gives the window a matchable app-id for the
+  # float+center+size windowrule (hyprland.nix); --gtk-single-instance=false
+  # forces a fresh standalone window (ghostty defaults single-instance on).
+  # calcurse ships uncommented in the downstream template (opt-out), so
+  # self-gate with a helpful notify if it's been removed. ghostty is always
+  # installed (ghostty.nix), so it can be relied on for the --class window.
+  calendarLauncher = pkgs.writeShellScriptBin "nomarchy-calendar" ''
+    if ! command -v calcurse >/dev/null 2>&1; then
+      notify-send "Calendar" "calcurse isn't installed (removed from home.packages?)." 2>/dev/null
+      exit 0
+    fi
+    exec ghostty --class=com.nomarchy.calendar --gtk-single-instance=false -e calcurse
+  '';
+
   # VPN indicator — shows a shield when a NetworkManager VPN/WireGuard
   # connection is active OR Tailscale is up; prints nothing otherwise so the
   # module self-hides (like nightlight/updates). Click opens the VPN submenu.
@@ -154,10 +170,13 @@ let
 
     clock = {
       format = "{:%H:%M}";
-      format-alt = "{:%A %d %B %Y}";
-      # Zone line first (LATER nicety): under auto-timezone the tz-watch
-      # SIGUSR2 reload keeps it showing the currently *detected* zone.
-      tooltip-format = "{:%Z (UTC%z)}\n<tt><small>{calendar}</small></tt>";
+      # Left-click → the calendar (nomarchy-calendar → calcurse in a floating
+      # ghostty). Replaces the old format-alt date toggle; the long date now
+      # rides in the tooltip's first line, so nothing is lost on hover.
+      on-click = "nomarchy-calendar";
+      # The zone line stays live under auto-timezone (the tz-watch SIGUSR2
+      # reload keeps it showing the currently *detected* zone).
+      tooltip-format = "{:%A %d %B %Y}\n{:%Z (UTC%z)}\n<tt><small>{calendar}</small></tt>";
     };
 
     # Active keyboard layout (per focused device) — only placed in
@@ -431,5 +450,5 @@ in
   # whole-swap themes' static waybar.jsonc can exec them by name — plus
   # the supervisor hyprland.nix exec-onces.
   home.packages = lib.optionals config.nomarchy.waybar.enable
-    [ waybarSupervisor powerProfileStatus powerProfileCycle vpnStatus doctorStatus ];
+    [ waybarSupervisor powerProfileStatus powerProfileCycle vpnStatus doctorStatus calendarLauncher ];
 }