fix(BUY-66091): alias domain/original_price in MCP get_deals SELECT [SEV-1]

[BuyWhere]

SEV-1 fix — BUY-66091

Symptom: get_deals MCP tool returns column "domain" does not exist for every call (US first reported probe #338, 2026-08-04 06:28Z). Previously returned statement_timeout.

Root cause: handleGetDeals in api/src/routes/mcp.ts selected bare domain and original_price columns from products, but neither exists on that table:

• domain is on merchants (not products)
• original_price is a JSONB metadata key (not a column)

The regression was introduced in 1f84498 (BUY-64112, 2026-08-04), which flattened the deals query and dropped the aliasing that the REST /v1/products/deals handler (products.ts) and buildProduct (response.ts reads row.domain / row.original_price) both rely on.

Fix: alias the columns the same way the REST handler does:

- SELECT id, source, domain, url, title, price, original_price, ...
+ SELECT id, source AS domain, url, title, price,
+        (metadata->>'original_price')::numeric AS original_price, ...

Verification:

• tsc --noEmit — 0 errors
• Ran the corrected query against prod DB (US): returns real deals (Article.com, 84% discount) with domain + original_price populated

SELECT id, source AS domain, ..., (metadata->>'original_price')::numeric AS original_price,
       ..., discount_pct
FROM products
WHERE currency='USD' AND price > 0 AND is_active=true AND discount_pct >= 10 AND country_code='US'
ORDER BY discount_pct DESC NULLS LAST, updated_at DESC LIMIT 3;
 → 3 rows ✓

Deploy blocker: Railway deploy tokens are Unauthorized (BUY-56879) — agent cannot deploy. Needs merge + pipeline unblock, or human Railway redeploy of buywhere-api.

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