fix(web): unify overlay z-index, decouple Placement type, and improve animation a11y

- Add z-50 to all overlay Positioners so overlays inside a Dialog
  (e.g. Tooltip on a dialog button) are not clipped by its backdrop
- Replace @floating-ui/react Placement import with self-owned type
  definition to remove the transitive type dependency
- Change Dialog popup transition-all to explicit transition-[transform,scale,opacity]
  to avoid animating unintended CSS properties
- Add motion-reduce:transition-none to all animated overlay elements
  for prefers-reduced-motion compliance

web/app/components/base/ui/dialog/index.tsx

@@ -1,8 +1,10 @@
 'use client'
 
 // z-index strategy (relies on root `isolation: isolate` in layout.tsx):
-//   Tooltip / Popover / Dropdown — no z-index, DOM order is sufficient
-//   Dialog backdrop + popup — z-50, ensures modal covers non-modal portals
+//   All overlay primitives (Tooltip / Popover / Dropdown / Select / Dialog) — z-50
+//   Overlays share the same z-index; DOM order handles stacking when multiple are open.
+//   This ensures overlays inside a Dialog (e.g. a Tooltip on a dialog button) render
+//   above the dialog backdrop instead of being clipped by it.
 //   Toast — z-[99], always on top (defined in toast component)
 
 import { Dialog as BaseDialog } from '@base-ui/react/dialog'
@@ -31,14 +33,14 @@ export function DialogContent({
       <BaseDialog.Backdrop
         className={cn(
           'fixed inset-0 z-50 bg-background-overlay',
-          'transition-opacity duration-150 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0',
+          'transition-opacity duration-150 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0 motion-reduce:transition-none',
           overlayClassName,
         )}
       />
       <BaseDialog.Popup
         className={cn(
           'fixed left-1/2 top-1/2 z-50 max-h-[80dvh] w-[480px] max-w-[calc(100vw-2rem)] -translate-x-1/2 -translate-y-1/2 rounded-2xl border-[0.5px] border-components-panel-border bg-components-panel-bg p-6 shadow-xl',
-          'transition-all duration-150 data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0',
+          'transition-[transform,scale,opacity] duration-150 data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0 motion-reduce:transition-none',
           className,
         )}
       >

web/app/components/base/ui/dropdown-menu/index.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import type { Placement } from '@floating-ui/react'
+import type { Placement } from '@/app/components/base/ui/placement'
 import { Menu } from '@base-ui/react/menu'
 import * as React from 'react'
 import { parsePlacement } from '@/app/components/base/ui/placement'
@@ -64,13 +64,13 @@ function renderDropdownMenuPopup({
         align={align}
         sideOffset={sideOffset}
         alignOffset={alignOffset}
-        className={cn('outline-none', className)}
+        className={cn('z-50 outline-none', className)}
         {...positionerProps}
       >
         <Menu.Popup
           className={cn(
             'rounded-xl border-[0.5px] border-components-panel-border bg-components-panel-bg py-1 text-sm text-text-secondary shadow-lg',
-            'origin-[var(--transform-origin)] transition-[transform,scale,opacity] data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0',
+            'origin-[var(--transform-origin)] transition-[transform,scale,opacity] data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0 motion-reduce:transition-none',
             popupClassName,
           )}
           {...popupProps}

web/app/components/base/ui/placement.ts

@@ -1,15 +1,26 @@
-import type { Placement } from '@floating-ui/react'
+// Placement type for overlay positioning.
+// Mirrors the Floating UI Placement spec — a stable set of 12 CSS-based position values.
+// Reference: https://floating-ui.com/docs/useFloating#placement
 
-type ParsedPlacement = {
-  side: 'top' | 'bottom' | 'left' | 'right'
-  align: 'start' | 'center' | 'end'
-}
+type Side = 'top' | 'bottom' | 'left' | 'right'
+type Align = 'start' | 'center' | 'end'
 
-export function parsePlacement(placement: Placement): ParsedPlacement {
-  const [side, align] = placement.split('-') as [
-    ParsedPlacement['side'],
-    ParsedPlacement['align'] | undefined,
-  ]
+export type Placement
+  = | 'top'
+    | 'top-start'
+    | 'top-end'
+    | 'right'
+    | 'right-start'
+    | 'right-end'
+    | 'bottom'
+    | 'bottom-start'
+    | 'bottom-end'
+    | 'left'
+    | 'left-start'
+    | 'left-end'
+
+export function parsePlacement(placement: Placement): { side: Side, align: Align } {
+  const [side, align] = placement.split('-') as [Side, Align | undefined]
 
   return {
     side,

web/app/components/base/ui/popover/index.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import type { Placement } from '@floating-ui/react'
+import type { Placement } from '@/app/components/base/ui/placement'
 import { Popover as BasePopover } from '@base-ui/react/popover'
 import * as React from 'react'
 import { parsePlacement } from '@/app/components/base/ui/placement'
@@ -48,13 +48,13 @@ export function PopoverContent({
         align={align}
         sideOffset={sideOffset}
         alignOffset={alignOffset}
-        className={cn('outline-none', className)}
+        className={cn('z-50 outline-none', className)}
         {...positionerProps}
       >
         <BasePopover.Popup
           className={cn(
             'rounded-xl border-[0.5px] border-components-panel-border bg-components-panel-bg shadow-lg',
-            'origin-[var(--transform-origin)] transition-[transform,scale,opacity] data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0',
+            'origin-[var(--transform-origin)] transition-[transform,scale,opacity] data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0 motion-reduce:transition-none',
             popupClassName,
           )}
           {...popupProps}

web/app/components/base/ui/select/index.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import type { Placement } from '@floating-ui/react'
+import type { Placement } from '@/app/components/base/ui/placement'
 import { Select as BaseSelect } from '@base-ui/react/select'
 import * as React from 'react'
 import { parsePlacement } from '@/app/components/base/ui/placement'
@@ -77,13 +77,13 @@ export function SelectContent({
         align={align}
         sideOffset={sideOffset}
         alignOffset={alignOffset}
-        className={cn('outline-none', className)}
+        className={cn('z-50 outline-none', className)}
         {...positionerProps}
       >
         <BaseSelect.Popup
           className={cn(
             'rounded-xl border-[0.5px] border-components-panel-border bg-components-panel-bg shadow-lg',
-            'origin-[var(--transform-origin)] transition-[transform,scale,opacity] data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0',
+            'origin-[var(--transform-origin)] transition-[transform,scale,opacity] data-[ending-style]:scale-95 data-[starting-style]:scale-95 data-[ending-style]:opacity-0 data-[starting-style]:opacity-0 motion-reduce:transition-none',
             popupClassName,
           )}
           {...popupProps}

web/app/components/base/ui/tooltip/index.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import type { Placement } from '@floating-ui/react'
+import type { Placement } from '@/app/components/base/ui/placement'
 import { Tooltip as BaseTooltip } from '@base-ui/react/tooltip'
 import * as React from 'react'
 import { parsePlacement } from '@/app/components/base/ui/placement'
@@ -37,7 +37,7 @@ export function TooltipContent({
         align={align}
         sideOffset={sideOffset}
         alignOffset={alignOffset}
-        className={cn('outline-none', className)}
+        className={cn('z-50 outline-none', className)}
       >
         <BaseTooltip.Popup
           className={cn(