fix: portal FilterPill popover so it escapes overflow clipping

The FilterBar uses overflow-x-auto for horizontal scroll, which forces
overflow-y to auto as well — that was clipping the absolutely-positioned
pill popovers below the bar. Render the popover into document.body via a
portal with fixed coordinates derived from getBoundingClientRect(), and
clamp the left edge so right-most pills don't push the popover off-screen.

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

frontend/src/components/filter/FilterPill.tsx

@@ -1,4 +1,5 @@
-import { useEffect, useRef, useState } from 'react'
+import { useEffect, useLayoutEffect, useRef, useState } from 'react'
+import { createPortal } from 'react-dom'
 import { ChevronDown, X } from 'lucide-react'
 import clsx from 'clsx'
 
@@ -17,9 +18,6 @@ interface FilterPillProps {
   children: React.ReactNode
   /** Force the popover open programmatically (rare). */
   defaultOpen?: boolean
-  /** Right-align the popover instead of left (for pills near the right
-   *  edge so they don't overflow the viewport). */
-  alignRight?: boolean
 }
 
 /**
@@ -35,19 +33,50 @@ export function FilterPill({
   onClear,
   children,
   defaultOpen = false,
-  alignRight = false,
 }: FilterPillProps) {
   const [open, setOpen] = useState(defaultOpen)
-  const wrapperRef = useRef<HTMLDivElement>(null)
+  const buttonRef = useRef<HTMLButtonElement>(null)
+  const popoverRef = useRef<HTMLDivElement>(null)
+  const [popoverPos, setPopoverPos] = useState<{ top: number; left: number } | null>(null)
 
-  // Close on outside click + Escape.
+  // Compute the popover's screen position from the trigger button. Done
+  // imperatively (not via CSS absolute) so the popover can live in a portal
+  // and escape the FilterBar's overflow-x-auto clipping. Re-computed on
+  // open, scroll, and resize.
+  useLayoutEffect(() => {
+    if (!open) return
+    const update = () => {
+      const btn = buttonRef.current
+      if (!btn) return
+      const rect = btn.getBoundingClientRect()
+      // Default left-align under the trigger; clamp to viewport so the
+      // last pill on the right doesn't overflow.
+      const popWidth = popoverRef.current?.offsetWidth ?? 240
+      const margin = 8
+      let left = rect.left
+      if (left + popWidth + margin > window.innerWidth) {
+        left = Math.max(margin, window.innerWidth - popWidth - margin)
+      }
+      setPopoverPos({ top: rect.bottom + 4, left })
+    }
+    update()
+    window.addEventListener('resize', update)
+    window.addEventListener('scroll', update, true)
+    return () => {
+      window.removeEventListener('resize', update)
+      window.removeEventListener('scroll', update, true)
+    }
+  }, [open])
+
+  // Close on outside click + Escape. Outside means neither the trigger
+  // button nor the (portaled) popover.
   useEffect(() => {
     if (!open) return
     const onDocMouseDown = (e: MouseEvent) => {
-      if (!wrapperRef.current) return
-      if (!wrapperRef.current.contains(e.target as Node)) {
-        setOpen(false)
-      }
+      const target = e.target as Node
+      if (buttonRef.current?.contains(target)) return
+      if (popoverRef.current?.contains(target)) return
+      setOpen(false)
     }
     const onKey = (e: KeyboardEvent) => {
       if (e.key === 'Escape') setOpen(false)
@@ -61,8 +90,9 @@ export function FilterPill({
   }, [open])
 
   return (
-    <div ref={wrapperRef} className="relative">
+    <>
       <button
+        ref={buttonRef}
         onClick={() => setOpen((v) => !v)}
         className={clsx(
           'flex items-center gap-1 rounded-full border px-2.5 py-1 text-xs transition-colors',
@@ -92,16 +122,22 @@ export function FilterPill({
         )}
       </button>
 
-      {open && (
-        <div
-          className={clsx(
-            'absolute top-full z-30 mt-1 min-w-[220px] rounded-lg border border-border bg-surface p-3 shadow-xl',
-            alignRight ? 'right-0' : 'left-0'
-          )}
-        >
-          {children}
-        </div>
-      )}
-    </div>
+      {open &&
+        createPortal(
+          <div
+            ref={popoverRef}
+            style={{
+              position: 'fixed',
+              top: popoverPos?.top ?? -9999,
+              left: popoverPos?.left ?? -9999,
+              visibility: popoverPos ? 'visible' : 'hidden',
+            }}
+            className="z-50 min-w-[220px] rounded-lg border border-border bg-surface p-3 shadow-xl"
+          >
+            {children}
+          </div>,
+          document.body
+        )}
+    </>
   )
 }