refactor(web): split TimelineContext into data, view, and display contexts

Reduces unnecessary re-renders by separating the monolithic 20+ property
context into TimelineDataContext, TimelineViewContext, and
TimelineDisplayContext. Panel components now subscribe only to the
slices they need.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/components/timeline/TimelineResourcePanel.tsx

@@ -3,7 +3,12 @@
 import { clsx } from "clsx";
 import { memo, startTransition, useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { useVirtualizer } from "@tanstack/react-virtual";
-import { useTimelineContext, type TimelineAssignmentEntry } from "./TimelineContext.js";
+import {
+  useTimelineData,
+  useTimelineView,
+  useTimelineDisplay,
+  type TimelineAssignmentEntry,
+} from "./TimelineContext.js";
 import { applyVisualOverrides, type TimelineVisualOverrides } from "./allocationVisualState.js";
 import { ConflictOverlay } from "./ConflictOverlay.js";
 import { computeSubLanes } from "./utils.js";
@@ -117,18 +122,9 @@ function TimelineResourcePanelInner({
   gridLines,
   xToDate,
 }: TimelineResourcePanelProps) {
-  const {
-    resources,
-    allocsByResource,
-    vacationsByResource,
-    filters,
-    viewStart,
-    viewEnd,
-    displayMode,
-    heatmapScheme,
-    blinkOverbookedDays,
-    activeFilterCount,
-  } = useTimelineContext();
+  const { resources, allocsByResource, vacationsByResource } = useTimelineData();
+  const { filters, viewStart, viewEnd, activeFilterCount } = useTimelineView();
+  const { displayMode, heatmapScheme, blinkOverbookedDays } = useTimelineDisplay();
 
   // ─── Heatmap hover state ────────────────────────────────────────────────────
   const heatmapRafRef = useRef<number | null>(null);