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/TimelineView.tsx

@@ -28,7 +28,8 @@ import { HEADER_DAY_HEIGHT, HEADER_MONTH_HEIGHT, LABEL_WIDTH } from "./timelineC
 import { formatDateShort } from "~/lib/format.js";
 import {
   TimelineProvider,
-  useTimelineContext,
+  useTimelineData,
+  useTimelineView,
   type TimelineAssignmentEntry,
 } from "./TimelineContext.js";
 import { TimelineResourcePanel } from "./TimelineResourcePanel.js";
@@ -339,17 +340,22 @@ function TimelineViewContent({
   undo: () => Promise<void>;
   redo: () => Promise<void>;
 }) {
-  const ctx = useTimelineContext();
   const {
     resources,
     projectGroups,
     allocsByResource,
     openDemandsByProject,
+    visibleAssignments,
+    visibleDemands,
+    isLoading,
+    isInitialLoading,
+    isEntriesError,
+    totalAllocCount,
+  } = useTimelineData();
+  const {
     viewStart,
     viewEnd,
     viewDays,
-    visibleAssignments,
-    visibleDemands,
     setViewStart,
     setViewDays,
     filters,
@@ -359,11 +365,7 @@ function TimelineViewContent({
     viewMode,
     setViewMode,
     today,
-    isLoading,
-    isInitialLoading,
-    isEntriesError,
-    totalAllocCount,
-  } = ctx;
+  } = useTimelineView();
 
   const scrollContainerRef = useRef<HTMLDivElement>(null);
   const canvasRef = useRef<HTMLDivElement>(null);