fix(purchase): match server-note resource heads to the providers' real type sets #1753

Summary

Follow-ups from the final reviews of #1739. The resource-type head allowed in front of a stored server note (resourceTypePattern, internal/purchase/errnotes.go ~:117-128) is still too narrow for some real types and too wide for some made-up tokens. Neither affects what users can see from a provider today, because the only writer of that head is internal/purchase/execution.go ~:763 with rec.ResourceType.

Too narrow: real types that fall back to the generic message

These ResourceType literals from cloud-commitments-go fall back to "the provider returned an error": Premium_P1, 100RU, Cosmos_DB_100_RUs, GeneralPurpose_Gen5_2, db-n1-standard-1, STANDARD, STANDARD_HA, BASIC, u7i-12tb.224xlarge and a3-edgegpu-8g. The impact is small: for non-EC2 types the only allowlisted per-rec note is "purchase was not successful", which the category message roughly matches. For EC2, u7i-* loses the zonal re-fetch hint.

Too wide: short tokens accepted as a head

• The unprefixed Azure alternative accepts DB1, SQL1 and PG01.
• The AWS grammar accepts web1.medium, db1.large and db.app1.large.
• The GCP grammar accepts n2-standard-db-prod and e2-micro-admin.

Expected

The accepted heads come from the providers' own resource-type sets wherever they are enumerable, and from grammars anchored to the real families where they are not (for example Azure sizes as [A-Z]{1,2}[0-9]{1,3}…). There is one test row per example above.

Related

#1739, #1748 (quoted value slots), #1721.