feat(waybar): add window title module and styled clock calendar

Center a `hyprland/window` title module and move the clock/date to the far
right of the bar. Give the clock a month-calendar tooltip with One Dark
Pango styling (yellow header, purple weekdays, blue underlined today, dim
ISO week-number gutter), 3-per-row year view via right-click.

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

modules/home.nix

@@ -655,15 +655,37 @@ in
         position = "top";
         height = 28;
         modules-left = [ "hyprland/workspaces" ];
-        modules-center = [ "clock" ];
+        modules-center = [ "hyprland/window" ];
-        modules-right = [ "pulseaudio" "network" "battery" ];
+        modules-right = [ "pulseaudio" "network" "battery" "clock" ];
 
         "hyprland/workspaces" = {
           format = "{id}";
         };
 
+        "hyprland/window" = {
+          format = "{title}";
+          max-length = 100;
+          separate-outputs = true;
+        };
+
         clock = {
           format = "{:%H:%M %a %d %b}";
+          tooltip-format = "<tt>{calendar}</tt>";
+          calendar = {
+            mode = "month";
+            mode-mon-col = 3;
+            weeks-pos = "left";
+            format = {
+              months   = "<span color='#e5c07b'><b>{}</b></span>";
+              weekdays = "<span color='#c678dd'><b>{}</b></span>";
+              days     = "<span color='#bbbbbb'>{}</span>";
+              today    = "<span color='#61afef'><b><u>{}</u></b></span>";
+              weeks    = "<span color='#5c6370'>W{:%V}</span>";
+            };
+          };
+          actions = {
+            on-click-right = "mode";
+          };
         };
 
         pulseaudio = {
@@ -703,9 +725,23 @@ in
         background: #222222;
         color: #bbbbbb;
       }
-      #pulseaudio, #network, #battery {
+      #pulseaudio, #network, #battery, #clock {
         padding: 0 12px;
       }
+      #window {
+        color: #ffffff;
+      }
+      tooltip {
+        background: #222222;
+        border: 1px solid #333333;
+      }
+      tooltip label {
+        font-size: 15px;
+        padding: 4px;
+      }
+      window#waybar.empty #window {
+        background: transparent;
+      }
       #battery.warning {
         color: #e5c07b;
       }

modules/nixos.nix

@@ -45,7 +45,7 @@
   time.timeZone = "Europe/Berlin";
 
   # Internationalisation properties. Template defaults — override per region.
-  i18n.defaultLocale = "en_US.UTF-8";
+  i18n.defaultLocale = lib.mkDefault "en_US.UTF-8";
   console = {
     font = "Lat2-Terminus16";
     keyMap = "de";