Azure recommendations missing no-upfront (monthly) payment variants

[cristim]

Summary

Azure reservation recommendations surface only the All-Upfront variant; the Monthly (no-upfront) payment option is missing across the UI even though Azure supports both billing plans for every reservation SKU.

Repro

1. Add an Azure subscription with reservation-eligible workloads (VMs, SQL DBs, Cache for Redis, etc).
2. Open the Recommendations page filtered to provider=Azure.
3. Every row shows PaymentOption = "upfront". There is no corresponding no-upfront / monthly row for the same SKU/term.

Root cause

Every Azure recommendation emission path hardcodes PaymentOption: "upfront" and emits a single variant per (account, region, SKU, term). Confirmed call sites:

• providers/azure/recommendations.go:144 (Azure Advisor adapter)
• providers/azure/services/compute/client.go:496 (convertAzureVMRecommendation)
• providers/azure/services/database/client.go:511
• providers/azure/services/cache/client.go:504
• (likely) providers/azure/services/cosmosdb/client.go, providers/azure/services/search/client.go, providers/azure/services/synapse/client.go, providers/azure/services/managedredis/client.go, providers/azure/services/savingsplans/client.go

pkg/common/types.go:101 already declares the canonical option set as "all-upfront, partial, no-upfront, monthly", so the schema supports the missing variants. Azure itself supports two billing plans per reservation: Upfront (one payment) and Monthly (twelve / thirty-six equal payments, no partial-upfront). Currently the converter emits a single hardcoded "upfront" value and never fans out.

Fix shape

For each Azure recommendation source, emit two common.Recommendation rows per (account, region, SKU, term):

1. PaymentOption = "all-upfront" (current behaviour, but canonical string instead of plain "upfront")
2. PaymentOption = "no-upfront" (Azure Monthly billing plan)

The two rows must carry separate pricing fields. Azure typically charges the same total reservation price for both plans, but per-period cashflow differs — UpfrontCost, RecurringMonthlyCost, and EstimatedSavings need to be computed per plan. The pricing helper should accept paymentOption and return the correct triple, mirroring the AWS service-clients' three-variant fan-out (all-upfront / partial / no-upfront).

Tests: extend each service client's table-driven recommendation test to assert that both all-upfront and no-upfront rows are produced per source row, and that UpfrontCost == 0 on the no-upfront variant.

Scope

Backend-only. Frontend already supports filtering by PaymentOption per the existing all-upfront rows, so additional rows will surface automatically through the same UI.

[cristim]

Verified shipped on feat/multicloud-web-frontend via PR #682 (merged 2026-05-22). Azure reservation recommendations now expand into both all-upfront and no-upfront (monthly) payment variants with canonical PaymentOption values.