feat: timeline multi-select, demand popover, resource hover card, merged tooltips, dark mode fixes

Major timeline enhancements:
- Right-click drag multi-selection with floating action bar (batch delete/assign)
- DemandPopover for demand strip details (replaces broken "Loading" modal)
- ResourceHoverCard on name hover showing skills, rates, role, chapter
- Merged heatmap+vacation tooltips into unified TimelineTooltip component
- Fixed overbooking blink animation (date normalization, z-index ordering)
- Fixed dark mode sticky column bleed-through in project view
- System roles admin page, notification task management, performance review docs

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

apps/web/src/hooks/useAppPreferences.ts

@@ -18,6 +18,8 @@ export interface AppPreferences {
   heatmapColorScheme: HeatmapColorScheme;
   /** Show open demand / placeholder entries by default when loading the timeline. Default: true. */
   showDemandProjects: boolean;
+  /** Blink overbooked days (>8h) as a warning on the timeline. Default: false. */
+  blinkOverbookedDays: boolean;
 }
 
 const STORAGE_KEY = "planarchy_prefs";
@@ -28,6 +30,7 @@ const DEFAULT: AppPreferences = {
   timelineDisplayMode: "strip",
   heatmapColorScheme: "green-red",
   showDemandProjects: true,
+  blinkOverbookedDays: false,
 };
 
 export function readAppPreferences(): AppPreferences {
@@ -94,5 +97,13 @@ export function useAppPreferences() {
     });
   }, []);
 
-  return { prefs, setHideCompletedProjects, setTimelineDisplayMode, setHeatmapColorScheme, setShowDemandProjects };
+  const setBlinkOverbookedDays = useCallback((value: boolean) => {
+    setPrefs((prev) => {
+      const next = { ...prev, blinkOverbookedDays: value };
+      saveAppPreferences(next);
+      return next;
+    });
+  }, []);
+
+  return { prefs, setHideCompletedProjects, setTimelineDisplayMode, setHeatmapColorScheme, setShowDemandProjects, setBlinkOverbookedDays };
 }