feat(02-03): install @radix-ui/react-tabs, add getClientFullDetail, create Server Actions

- Add shadcn tabs component (src/components/ui/tabs.tsx) backed by @radix-ui/react-tabs
- Extend admin-queries.ts with getClientFullDetail() — fetches client + phases + tasks + deliverables + payments + documents + notes + comments in one call
- Create src/app/admin/clients/[id]/actions.ts with all mutations: addPhase, updatePhaseStatus, addTask, updateTaskStatus, addDeliverable, addDocument, deleteDocument, updatePaymentStatus, updateAcceptedTotal, postAdminComment
- All actions include server-side allowlist validation and revalidatePath
- approved_at immutability enforced by omission in addDeliverable

package.json

@@ -15,6 +15,7 @@
     "@radix-ui/react-select": "^2.2.6",
     "@radix-ui/react-separator": "^1.1.8",
     "@radix-ui/react-slot": "^1.2.4",
+    "@radix-ui/react-tabs": "^1.1.13",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "drizzle-orm": "^0.45.2",