ops(gcp): fix Compute permission issue for serene-bazaar-666 or downgrade log level

[cristim]

GCP account serene-bazaar-666 is missing 'compute.regions.list' permission.

Visible in production Lambda logs:
[ERROR] GCP account GCP serene-bazaar-666 (serene-bazaar-666): get recommendations: failed to get regions: failed to list regions: googleapi: Error 403: Required 'compute.regions.list' permission for 'projects/serene-bazaar-666'

Two paths to fix:

• Operator action (preferred): grant the GCP service account 'roles/compute.viewer' on the project.
• Code-side mitigation: the collector could downgrade to [WARN] for permission errors specifically.

The collector's account-failure-swallow bug masks this entirely: the GCP provider is reported as successful even when this account fails.

[cristim]

Verified shipped: merge commit 0ffdb96 (PR #585) is in origin/feat/multicloud-web-frontend (compare API: feat is ahead of 0ffdb96). PR #585 body says "Closes #247" and downgrades the GCP compute.regions.list 403 error to a Warn log, returning empty recs rather than propagating the error.