Add ExpectedAsset CSV import + bot search/pick for pre-known inventory

Lets the operator upload a CSV of already-known assets (asset tag, model,
serial, old area/assignee) before an office-move walk, via a new
session-authed /inventory-scans/import page. The Telegram bot gains a
"tim trong list" search step at the asset-tag prompt: picking a match
pre-fills tag/serial and offers one-tap "giu nguyen" buttons for the
old area/assignee, then marks that row matched once the scan is created.

Follows the same-day decision to turn off local OCR (qwen2.5vl via Ollama)
for this feature -- see CLAUDE.md and the ITAM/Ollama vault notes for the
accuracy/speed numbers behind that call.

Deviates from repo convention same as the InventoryScan work above: no
Vitest coverage (manual smoke test only, via simulated webhook calls),
hand-written migration, not through the ba->pm->feature-implementer->
test-runner->code-reviewer pipeline. tsc/lint are clean.

prisma/migrations/20260821194252_add_expected_asset/migration.sql

@@ -0,0 +1,19 @@
+-- Hand-written (same deviation as the other 2026-08-20 migrations in this
+-- feature -- see CLAUDE.md "Việc còn dở"), not `prisma migrate dev`.
+CREATE TABLE "expected_assets" (
+    "id" UUID NOT NULL,
+    "asset_tag" TEXT,
+    "model_text" TEXT NOT NULL,
+    "serial_number" TEXT,
+    "old_area_text" TEXT,
+    "old_assignee_text" TEXT,
+    "matched_scan_id" UUID,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "expected_assets_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX "expected_assets_matched_scan_id_key" ON "expected_assets"("matched_scan_id");
+
+ALTER TABLE "expected_assets" ADD CONSTRAINT "expected_assets_matched_scan_id_fkey"
+    FOREIGN KEY ("matched_scan_id") REFERENCES "inventory_scans"("id") ON DELETE SET NULL ON UPDATE CASCADE;