fix(timeline): clear multi-select on drag start and lock in SSE edge-case coverage

- useTimelineDrag: onProjectBarMouseDown and single-alloc drag path now reset
  multiSelectRef + multiSelectState before starting a new drag, so the
  FloatingActionBar is dismissed immediately when an unrelated drag begins
- FloatingActionBar.test.tsx: 4 regression tests for the null-render guard
  (count=0) and all three label variants
- useTimelineSSE.test.ts: 2 new tests — tab hides during pending reconnect
  timer (clears timer, resyncs on next open) and first-ever connection fails
  before any open (retry open still resyncs correctly)
- assistant-tools-user-admin-inventory-read.test.ts: add isActive to expected
  findMany select shape (already in production, test was stale)

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

apps/web/src/hooks/useTimelineDrag.ts

@@ -496,6 +496,8 @@ export function useTimelineDrag({
       },
     ) => {
       if (e.button !== 0) return;
+      multiSelectRef.current = INITIAL_MULTI_SELECT;
+      setMultiSelectState(INITIAL_MULTI_SELECT);
       e.preventDefault();
       e.stopPropagation();
       const state = createProjectDragState<DragState>({
@@ -610,6 +612,8 @@ export function useTimelineDrag({
 
       // ── Single allocation drag ────────────────────────────────────────────
 
+      multiSelectRef.current = INITIAL_MULTI_SELECT;
+      setMultiSelectState(INITIAL_MULTI_SELECT);
       const initial = createAllocationDragState<AllocDragState, AllocDragMode, AllocDragScope>({
         mode: opts.mode,
         scope: opts.scope,