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/components/layout/PreferencesModal.tsx

@@ -20,7 +20,7 @@ const ACCENT_OPTIONS: { value: AccentColor; label: string; swatch: string }[] =
 
 export function PreferencesModal({ onClose }: PreferencesModalProps) {
   const { prefs, setMode, setAccent } = useTheme();
-  const { prefs: appPrefs, setHideCompletedProjects, setTimelineDisplayMode, setHeatmapColorScheme, setShowDemandProjects } = useAppPreferences();
+  const { prefs: appPrefs, setHideCompletedProjects, setTimelineDisplayMode, setHeatmapColorScheme, setShowDemandProjects, setBlinkOverbookedDays } = useAppPreferences();
 
   return (
     <div
@@ -219,6 +219,34 @@ export function PreferencesModal({ onClose }: PreferencesModalProps) {
               </div>
             </div>
 
+            {/* Overbooked blink */}
+            <label className="flex items-start gap-3 cursor-pointer mb-3">
+              <div className="relative mt-0.5 flex-shrink-0">
+                <input
+                  type="checkbox"
+                  checked={appPrefs.blinkOverbookedDays}
+                  onChange={(e) => setBlinkOverbookedDays(e.target.checked)}
+                  className="sr-only peer"
+                />
+                <div className={clsx(
+                  "w-9 h-5 rounded-full transition-colors",
+                  appPrefs.blinkOverbookedDays ? "bg-brand-600" : "bg-gray-200 dark:bg-gray-700",
+                )} />
+                <div className={clsx(
+                  "absolute top-0.5 left-0.5 w-4 h-4 bg-white rounded-full shadow transition-transform",
+                  appPrefs.blinkOverbookedDays ? "translate-x-4" : "translate-x-0",
+                )} />
+              </div>
+              <div>
+                <span className="text-sm text-gray-800 dark:text-gray-200 font-medium leading-tight block">
+                  Blink overbooked days
+                </span>
+                <span className="text-xs text-gray-400 dark:text-gray-500">
+                  Highlight days where a resource exceeds 8h with a pulsing animation.
+                </span>
+              </div>
+            </label>
+
             <label className="flex items-start gap-3 cursor-pointer">
               <div className="relative mt-0.5 flex-shrink-0">
                 <input