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/components/timeline/FloatingActionBar.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import React from "react";
 import { clsx } from "clsx";
 
 interface FloatingActionBarProps {