fix(ui): theme popover/input tokens and open select below trigger

Select dropdowns (voice tab, guild selector) rendered with a transparent
background because --color-popover/--color-input were undefined, and the
popup overlapped the trigger due to alignItemWithTrigger. Define the missing
theme tokens (popover, popover-foreground, input, secondary) and default the
select popup to open below the trigger.

services/frontend/src/app/globals.css

@@ -56,6 +56,13 @@
   /* Ring / focus outline for shadcn outline-ring utility */
   --color-ring: var(--color-primary);
 
+  /* Base-ui / shadcn primitives */
+  --color-popover: oklch(0.99 0.005 250 / 0.95);
+  --color-popover-foreground: var(--color-text-primary);
+  --color-input: oklch(0.55 0.02 250 / 0.35);
+  --color-secondary: oklch(0.92 0.01 250 / 0.6);
+  --color-secondary-foreground: var(--color-text-primary);
+
   /* Sidebar (shadcn) */
   --color-sidebar: oklch(1 0 0 / 0.6);
   --color-sidebar-foreground: var(--color-text-primary);
@@ -113,6 +120,13 @@
   --color-accent-foreground: var(--color-primary-foreground);
   --color-ring: var(--color-primary);
 
+  /* Base-ui / shadcn primitives */
+  --color-popover: oklch(0.13 0.02 245 / 0.96);
+  --color-popover-foreground: var(--color-text-primary);
+  --color-input: oklch(1 0 0 / 0.18);
+  --color-secondary: oklch(0.2 0.02 245 / 0.7);
+  --color-secondary-foreground: var(--color-text-primary);
+
   /* Sidebar (shadcn) */
   --color-sidebar: oklch(0.11 0.02 245 / 0.55);
   --color-sidebar-foreground: var(--color-text-primary);

services/frontend/src/components/ui/select.tsx

@@ -63,7 +63,7 @@ function SelectContent({
   sideOffset = 4,
   align = "center",
   alignOffset = 0,
-  alignItemWithTrigger = true,
+  alignItemWithTrigger = false,
   ...props
 }: SelectPrimitive.Popup.Props &
   Pick<