feat(frontend/recs): render Azure Savings Plans rows + column visibility in recommendations table

[cristim]

PR #592 wired the Azure Savings Plans provider.ServiceClient (list commitments, purchase, validate offerings) and its dispatch, but explicitly deferred the frontend work: the Opportunities/recommendations table has no column visibility or row rendering for Azure Savings Plans recommendations.

PR #592 listed this under "Out of scope (follow-up issues filed below)" but the issue was never actually filed (only the scheduler-wiring follow-up LeanerCloud/cloud-commitments-platform#17 was). Filing it now to capture the gap.

Scope:

• Surface Azure Savings Plans rows in the recommendations table (rendering + any provider/service-specific columns).
• Mirror the existing AWS Savings Plans column/visibility handling where applicable.

Out of scope when deferred: PR #592 was scoped to the backend provider client + dispatch wiring only; frontend rendering is a separate surface.

Deferred by: #592
Related: LeanerCloud/cloud-commitments-platform#17 (scheduler wiring), #554 (Azure SP support epic), #473 (AWS to Azure parity).

[cristim]

Verified shipped on feat/multicloud-web-frontend via PR #723 (merged 2026-05-27). isSavingsPlanService in recommendations.ts now matches both 'savings-plans' (hyphenated) and 'savingsplans' (no hyphen) so Azure SP rows are included in the service-column group and column visibility works correctly.