refactor(web): drop the availability missing-column fallback from #1164 #1174

Follow-up from #1164 and #1147.

Problem

#1164 added a fallback to the rate.products.availability read: when the read fails or the column is missing (the E2E schema before #1147), it logs one warning and leaves availability unknown. #1147 (PR #1169) mirrored the DOS-Me migrations into the reference schema, so E2E now has the column and the fallback only hides real errors.

Task

• Remove the missing-column branch of the availability fallback in apps/web (single-product and, if fix(web): category deal radar reads listing availability (sold-out offers still cited) #1170 has landed, batch reads). A failed read should surface like the other required reads.
• Update the tests that pinned the fallback.

Acceptance

• No code path treats a missing availability column as expected.
• Typecheck, unit tests and E2E (Playwright) green.

Depends on #1169 (merged).