feat: Dispo V2 import — API router + admin UI

API Router (packages/api/src/router/dispo.ts):
- 12 adminProcedure endpoints wired to existing application layer
- stageImportBatch, validateImportBatch, commitImportBatch
- listImportBatches, getImportBatch, cancelImportBatch
- listStagedResources/Projects/Assignments/Vacations/Unresolved
- resolveStagedRecord (APPROVE/REJECT/SKIP actions)

Admin UI:
- /admin/dispo-imports — batch list with status filter, new import modal
- /admin/dispo-imports/[batchId] — detail with 6 tabs:
  Summary, Resources, Projects, Assignments, Vacations, Unresolved
- Unresolved review queue with approve/skip per-record actions
- Commit workflow with pre-validation and progress indicator
- Sidebar nav link under Admin

Also fixes: timeline filter dropdown z-index (toolbar relative z-20)

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

apps/web/src/components/layout/AppShell.tsx

@@ -189,6 +189,7 @@ const adminNavEntries: AdminEntry[] = [
   { href: "/admin/skill-import", label: "Skill Import", icon: <AdminIcon /> },
   { href: "/admin/notifications", label: "Broadcasts", icon: <BroadcastIcon /> },
   { href: "/admin/webhooks", label: "Webhooks", icon: <AdminIcon /> },
+  { href: "/admin/dispo-imports", label: "Dispo Import", icon: <AdminIcon /> },
 ];
 
 /**