waybar: fix GTK3 CSS variables, pin timezone, adjust screenshot keybind

- theme/colors.css: replace CSS custom properties (--var) with GTK3
  @define-color — GTK3 CSS parser rejects -- syntax, crashing waybar
- waybar/style.css, wofi/style.css, gtklock/style.css: update var(--x)
  references to @x to match
- waybar/config.jsonc: pin clock timezone to America/Vancouver
- niri/config.kdl: change Print to Mod+Print for screenshot keybind

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wofi/style.css

@@ -6,26 +6,26 @@
 }
 
 window {
-  background-color: var(--tn-bg-a96);
-  border: 1px solid var(--tn-bg-high);
+  background-color: @tn-bg-a96;
+  border: 1px solid @tn-bg-high;
   border-radius: 12px;
-  color: var(--tn-fg);
+  color: @tn-fg;
 }
 
 #input {
-  background-color: var(--tn-bg-alt);
-  color: var(--tn-fg);
-  border: 1px solid var(--tn-bg-high);
+  background-color: @tn-bg-alt;
+  color: @tn-fg;
+  border: 1px solid @tn-bg-high;
   border-radius: 8px;
   padding: 10px 14px;
   margin: 12px 12px 6px 12px;
   outline: none;
   font-size: 15px;
-  caret-color: var(--tn-blue);
+  caret-color: @tn-blue;
 }
 
 #input:focus {
-  border-color: var(--tn-blue);
+  border-color: @tn-blue;
 }
 
 #inner-box {
@@ -48,17 +48,17 @@ window {
 }
 
 #entry:selected {
-  background-color: var(--tn-bg-alt);
-  border: 1px solid var(--tn-blue);
+  background-color: @tn-bg-alt;
+  border: 1px solid @tn-blue;
   outline: none;
 }
 
 #text {
-  color: var(--tn-fg);
+  color: @tn-fg;
 }
 
 #text:selected {
-  color: var(--tn-blue);
+  color: @tn-blue;
   font-weight: bold;
 }