fix: lock filter bar height + freeze pill positions

- FilterPill: fixed h-7 + py-0 on the button so neither the X clear icon
  nor the chevron can stretch the pill vertically when active state
  swaps them in. The chevron is now wrapped in the same h-4 w-4 slot as
  the clear X so swapping doesn't change footprint horizontally either.
- FilterBar: fixed h-11 on the bar itself so any future per-pill drift
  can't grow the row.
- Clear-all: wrapped in a fixed w-56 right slot that mirrors the search
  input on the left. The pill cluster sits in the centered flex-1
  middle slot, so it stays perfectly centered whether or not Clear-all
  is rendered. The button itself is right-aligned within the slot.

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

frontend/src/components/filter/FilterBar.tsx

@@ -116,7 +116,10 @@ export function FilterBar() {
   const anyActive = hasActiveFilters(filterState)
 
   return (
-    <div className="flex items-center gap-3 border-b border-border bg-surface px-3 py-1.5">
+    // Fixed bar height + py-0 so neither the active filter pills nor the
+    // clear-all button can stretch the bar vertically. The fixed h-11
+    // matches the h-7 pills + 8px symmetric vertical padding.
+    <div className="flex h-11 items-center gap-3 border-b border-border bg-surface px-3 py-0">
       {/* Search — left of the pill cluster. Same id as before so the
        *  global "/" focus shortcut still finds it. */}
       <div className="relative w-56 flex-shrink-0">
@@ -377,16 +380,21 @@ export function FilterBar() {
       </FilterPill>
       </div>
 
-      {/* Clear-all — pinned right of the pill cluster. */}
-      {anyActive && (
-        <button
-          onClick={clearAll}
-          className="flex-shrink-0 whitespace-nowrap rounded-full border border-border px-2.5 py-1 text-xs text-text-muted hover:bg-surface-2 hover:text-text"
-          title="Clear all filters in this section"
-        >
-          Clear all
-        </button>
-      )}
+      {/* Right slot — fixed-width so the pill cluster stays perfectly
+       *  centered in the bar regardless of whether Clear-all is visible.
+       *  Width matches the search input on the left for symmetric
+       *  framing. The button itself is right-aligned within the slot. */}
+      <div className="flex w-56 flex-shrink-0 justify-end">
+        {anyActive && (
+          <button
+            onClick={clearAll}
+            className="flex h-7 items-center whitespace-nowrap rounded-full border border-border px-2.5 text-xs text-text-muted hover:bg-surface-2 hover:text-text"
+            title="Clear all filters in this section"
+          >
+            Clear all
+          </button>
+        )}
+      </div>
     </div>
   )
 }

frontend/src/components/filter/FilterPill.tsx

@@ -100,7 +100,10 @@ export function FilterPill({
         // canonical place to read/edit the filter value.
         title={isActive && value ? `${label}: ${value}` : label}
         className={clsx(
-          'flex items-center gap-1 rounded-full border px-2.5 py-1 text-xs transition-colors',
+          // Fixed height + py-0 so neither the X clear icon nor the
+          // chevron can stretch the pill vertically when the active
+          // state swaps them in.
+          'flex h-7 items-center gap-1 rounded-full border px-2.5 py-0 text-xs transition-colors',
           isActive
             ? 'border-primary/40 bg-primary/15 text-primary'
             : 'border-border bg-surface-2 text-text-muted hover:bg-surface-offset hover:text-text'
@@ -122,14 +125,18 @@ export function FilterPill({
                 onClear()
               }
             }}
-            className="ml-1 inline-flex h-5 w-5 cursor-pointer items-center justify-center rounded-full hover:bg-primary/30"
+            // Same h-4 w-4 as the chevron slot below so swapping the
+            // two doesn't change the pill's footprint.
+            className="ml-0.5 inline-flex h-4 w-4 cursor-pointer items-center justify-center rounded-full hover:bg-primary/30"
             title={`Clear ${label}`}
             aria-label={`Clear ${label}`}
           >
             <X className="h-3 w-3" />
           </span>
         ) : (
-          <ChevronDown className="h-3 w-3 opacity-60" />
+          <span className="inline-flex h-4 w-4 items-center justify-center">
+            <ChevronDown className="h-3 w-3 opacity-60" />
+          </span>
         )}
       </button>