🤖 fix: correct z-index layering for dialogs and UI elements (#1024)

_Generated with `mux`_

Fixes toast appearing over the Secrets modal dialog by correcting
z-index layering.

### Changes
- Dialog overlay and content: `z-50` → `z-[1500]` (above toasts)
- ModelSelector: `z-[1000]` → `z-[1020]` (above command suggestions)

### Z-index hierarchy
| z-index | Component |
|---------|-----------|
| `z-[1000]` | ChatInputToast |
| `z-[1010]` | CommandSuggestions |
| `z-[1020]` | ModelSelector |
| `z-[1500]` | Dialog |
| `z-[2000]` | CommandPalette |
| `z-[9999]` | TutorialTooltip |
| `z-[10000]` | KebabMenu, PopoverError |

Author: ibetitsmike

src/browser/components/ModelSelector.tsx

@@ -243,7 +243,7 @@ export const ModelSelector = forwardRef<ModelSelectorRef, ModelSelectorProps>(
           )}
         </div>
         {showDropdown && (
-          <div className="bg-separator border-border-light absolute bottom-full left-0 z-[1000] mb-1 max-h-[200px] min-w-80 overflow-y-auto rounded border shadow-[0_4px_12px_rgba(0,0,0,0.3)]">
+          <div className="bg-separator border-border-light absolute bottom-full left-0 z-[1020] mb-1 max-h-[200px] min-w-80 overflow-y-auto rounded border shadow-[0_4px_12px_rgba(0,0,0,0.3)]">
             {filteredModels.length === 0 ? (
               <div className="text-muted-light font-monospace px-2.5 py-1.5 text-[11px]">
                 No matching models

src/browser/components/ui/dialog.tsx

@@ -26,7 +26,7 @@ const DialogOverlay = React.forwardRef<
   <DialogPrimitive.Overlay
     ref={ref}
     className={cn(
-      "fixed inset-0 z-50 bg-black/50 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0",
+      "fixed inset-0 z-[1500] bg-black/50 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0",
       className
     )}
     {...props}
@@ -50,7 +50,7 @@ const DialogContent = React.forwardRef<
     <DialogPrimitive.Content
       ref={ref}
       className={cn(
-        "bg-dark border-border fixed top-[50%] left-[50%] z-50 grid w-[90%] translate-x-[-50%] translate-y-[-50%] gap-4 rounded-lg border p-6 shadow-lg duration-200 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 data-[state=closed]:slide-out-to-left-1/2 data-[state=closed]:slide-out-to-top-[48%] data-[state=open]:slide-in-from-left-1/2 data-[state=open]:slide-in-from-top-[48%]",
+        "bg-dark border-border fixed top-[50%] left-[50%] z-[1500] grid w-[90%] translate-x-[-50%] translate-y-[-50%] gap-4 rounded-lg border p-6 shadow-lg duration-200 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 data-[state=closed]:slide-out-to-left-1/2 data-[state=closed]:slide-out-to-top-[48%] data-[state=open]:slide-in-from-left-1/2 data-[state=open]:slide-in-from-top-[48%]",
         !maxWidth && "max-w-lg",
         maxHeight && "overflow-y-auto",
         className