fix(timeline): stabilize popovers on internal scroll + expand test coverage

B-1: useViewportPopover — ignoreScrollContainers option; scroll events
originating inside the timeline canvas no longer close point-anchor popovers
B-2: AllocationPopover, DemandPopover, NewAllocationPopover — thread
scrollContainerRef through so horizontal timeline scroll is ignored
B-3: AllocationPopover — staleTime 0 so SSE reconnect triggers immediate refetch
B-4: useViewportPopover.test.ts — 6 new tests (scroll close, ignore container,
resize close, style clamping)
B-5: AllocationPopover.test.tsx — loading state + happy-path tests added

Co-Authored-By: claude-flow <ruv@ruv.net>

apps/web/src/hooks/useViewportPopover.ts

@@ -1,4 +1,4 @@
-import { useEffect, useRef, useState, type CSSProperties } from "react";
+import React, { useEffect, useRef, useState, type CSSProperties } from "react";
 
 type PopoverAnchor =
   | { kind: "point"; x: number; y: number }
@@ -18,6 +18,7 @@ interface UseViewportPopoverOptions {
   viewportPadding?: number;
   ignoreElements?: Array<HTMLElement | null>;
   ignoreSelectors?: string[];
+  ignoreScrollContainers?: React.RefObject<HTMLElement | null>[];
   zIndex?: number;
 }
 
@@ -32,6 +33,7 @@ export function useViewportPopover({
   viewportPadding = 16,
   ignoreElements = [],
   ignoreSelectors = [],
+  ignoreScrollContainers,
   zIndex = 9998,
 }: UseViewportPopoverOptions) {
   const ref = useRef<HTMLDivElement>(null);
@@ -182,8 +184,19 @@ export function useViewportPopover({
 
     updateOrClose();
 
-    const handleScroll = () => {
+    const handleScroll = (event: Event) => {
       if (closeOnViewportChange) {
+        const scrollTarget = (event as Event).target;
+        if (
+          ignoreScrollContainers?.some(
+            (r) =>
+              r.current != null &&
+              scrollTarget instanceof Node &&
+              r.current.contains(scrollTarget),
+          )
+        ) {
+          return;
+        }
         cancelScheduledFrame();
         onClose();
         return;
@@ -215,6 +228,7 @@ export function useViewportPopover({
     align,
     anchor,
     estimatedHeight,
+    ignoreScrollContainers,
     offset,
     onClose,
     side,