PRE-3603: Overload scalapay min/max amounts from API

[adumont-payplug]

Description

Scalapay currently shows at checkout for any cart amount within the limits reported by the PayPlug API, with no way for the merchant to tighten that range. This adds merchant-configurable min/max amount limits for Scalapay, mirroring the existing amount-filtering mechanism already used for the other PPRO gateways.

• Two new optional fields (min_amount, max_amount) on the Scalapay gateway admin config, rendered as MoneyType (EUR) inputs. Left blank, they fall back to whatever the PayPlug API reports for the account.
• SupportedMethodsProvider now applies the merchant's configured bounds (when set) instead of the raw API bounds when filtering Scalapay at checkout.
• A new save-time validator (IsScalapayAmountRangeValid) rejects configs where min > max, or where either value falls outside the live API-reported range — the merchant can only narrow the range, never widen it beyond what PayPlug authorizes.

Motivation: Merchants want to control which cart sizes see Scalapay as a payment option (UX and fee control), similar to existing carve-outs for other financing/BNPL methods.

Related issue(s): Closes [PRE-3603](https://payplug-prod.atlassian.net/browse/PRE-3603)

---

Type of Change

• ✨ New feature (non-breaking change that adds functionality)

---

Checklist

Code Quality

• Code is linted and formatted (ECS clean)
• No unnecessary commented-out code or debug logs
• No hardcoded values (bounds come from the live API, not hardcoded constants)

Testing

• Unit tests added / updated (SupportedMethodsProviderTest, PaymentMethodValidatorTest, new ScalapayGatewayConfigurationTypeExtensionTest, new IsScalapayAmountRangeValidValidatorTest)
• New/changed code is covered by tests

Security & Ops

• No sensitive data or secrets introduced
• Logging and error handling are appropriate (API failures during validation fail open — a transient PayPlug API error doesn't block saving the payment method; existing behavior for other save-time checks)

[hdelaforce-payplug]

Automated review pass — 7 findings, most severe first. #1 is the one I'd block merge on: it's a config the admin form actively allows the merchant to save, and it silently disables Scalapay at checkout with zero diagnostic.

[claude]

Claude Code Review

Claude Code Review is paused for this repository. To reconnect it, an admin of this repository's GitHub organization (or the account owner, for personal repositories) who can also manage your Claude organization's Code Review settings needs to re-link GitHub in Code Review settings. This is a one-time step.

_{Tip: disable this comment in your organization's Code Review settings.}