fix(ui): add dark mode styles to amber warning boxes app-wide

Amber alert boxes were missing dark: variants, rendering as muddy
dark-orange in dark mode with near-unreadable text. Fixed in:
- VacationClient (Pending Approvals banner)
- VacationModal (conflict warning)
- ResourceDetail (load error)
- SkillMatrixUpload (replace warning)
- AllocationModal (open demand toggle)
- ProjectWizard (budget bar, post-creation warnings)

Pattern: bg-amber-50 → dark:bg-amber-950/30, border-amber-200 →
dark:border-amber-800, text-amber-7/800 → dark:text-amber-300/400

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

apps/web/src/components/vacations/VacationClient.tsx

@@ -179,19 +179,19 @@ export function VacationClient() {
         <>
           {/* Pending approvals (manager view) */}
           {pendingList.length > 0 && (
-            <div className="bg-amber-50 border border-amber-200 rounded-xl p-4">
+            <div className="bg-amber-50 dark:bg-gray-800 border border-amber-200 dark:border-amber-700/50 rounded-xl p-4">
               <div className="flex items-center justify-between mb-3">
-                <h2 className="text-sm font-semibold text-amber-800">
+                <h2 className="text-sm font-semibold text-amber-800 dark:text-amber-400">
                   Pending Approvals ({pendingList.length})
                 </h2>
                 {/* Batch controls */}
                 <div className="flex items-center gap-2">
-                  <label className="flex items-center gap-1.5 text-xs text-amber-700 cursor-pointer">
+                  <label className="flex items-center gap-1.5 text-xs text-amber-700 dark:text-amber-400 cursor-pointer">
                     <input
                       type="checkbox"
                       checked={allPendingSelected}
                       onChange={toggleSelectAll}
-                      className="rounded border-amber-300 text-amber-600"
+                      className="rounded border-amber-300 dark:border-amber-600 text-amber-600"
                     />
                     Select all
                   </label>

apps/web/src/components/vacations/VacationModal.tsx

@@ -317,7 +317,7 @@ export function VacationModal({ resourceId: initialResourceId, onClose, onSucces
 
           {/* Conflict warning */}
           {existingVacations && existingVacations.length > 0 && (
-            <div className="rounded-lg bg-amber-50 border border-amber-200 px-4 py-3 text-sm text-amber-700">
+            <div className="rounded-lg bg-amber-50 dark:bg-amber-950/30 border border-amber-200 dark:border-amber-800 px-4 py-3 text-sm text-amber-700 dark:text-amber-300">
               <strong>Existing vacation in this period:</strong>
               <ul className="mt-1 space-y-0.5">
                 {existingVacations.map((v) => (