fix(recommendations): tell the user when GCP recommendations are skipped for a non-USD currency #1472

Problem: since the cloud-commitments-go bump in #1466, a GCP Compute Engine CUD recommendation whose cost projection isn't in USD is skipped. This follows the USD-only rule decided on go#124. The skip happens inside the library (convertOrSkipBadAmount in providers/gcp services/computeengine/client.go around line 467) and is only logged with log.Printf. The platform never learns that anything was dropped. A customer whose GCP billing account isn't in USD sees an empty or short Compute Engine list with no explanation. That breaks the fail-loud rule. The same path also drops recs with malformed amounts.

Fix:

1. Library (cloud-commitments-go): return the skipped count and reasons with the recommendations, for example a typed partial result or a skipped-count field on the response, instead of only logging them.
2. Platform: record the count per account and provider on the collection run. Show it to the user as a warning on the recommendations view, e.g. "3 GCP recommendations skipped: prices not in USD". It should behave the same as the existing Azure partial-subscription warning.

Add a scheduler test for a non-USD GCP rec that produces the warning.

This issue is blocked on the library change.