feat(ui): UI/UX polish — layout, sidebar, button, theme improvements

- Fix global scrollbar overflow by removing h-svh from html element
- Add h-full overflow-hidden to html/body for proper app-like layout
- Fix default button variant: add shadow-sm and hover:bg-primary/90
- Update sidebar create-issue button to bg-background with shadow
- Add WorkspaceAvatar component and search/new-issue actions to sidebar header
- Improve theme provider with TooltipProvider wrapper
- Polish various page layouts, pickers, modals, and code block styling
- Clean up custom.css unused styles

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/ui/src/components/ui/button.tsx

@@ -10,7 +10,7 @@ const buttonVariants = cva(
   {
     variants: {
       variant: {
-        default: "bg-primary text-primary-foreground [a]:hover:bg-primary/80",
+        default: "bg-primary text-primary-foreground shadow-sm hover:bg-primary/90",
         outline:
           "border-border bg-background hover:bg-muted hover:text-foreground aria-expanded:bg-muted aria-expanded:text-foreground dark:border-input dark:bg-input/30 dark:hover:bg-input/50",
         secondary:

packages/ui/src/styles/custom.css

@@ -107,11 +107,6 @@
   @apply w-full max-w-4xl mx-auto;
 }
 
-/* Sidebar: remove default padding from inset container */
-[data-slot="sidebar-container"] {
-  padding: 0 !important;
-}
-
 /* Tool status: running glow pulse */
 @keyframes glow-pulse {
   0%, 100% { box-shadow: 0 0 0 0 var(--tool-running); }