Add dnqr (DuitNow QR) payment method support

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Mirrors the proven chip-for-woocommerce dnqr resolver pattern.

• Adds dnqr (modern DuitNow QR) to the DuitNow QR group, interchangeable with legacy duitnow_qr.
• Merchant keeps selecting the single duitnow_qr entry; dnqr is resolved at runtime via /payment_methods/.
• Resolver: expand group in-memory → short-circuit if no group member → static cache (brand+currency+amount-bucket) → intersect with available methods → prioritize dnqr → fallback to expanded whitelist on API failure.

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Generalised the DuitNow QR resolver into resolve_payment_method_groups() to also handle the modern ShopeePay group.

• Added SHOPEE_GROUP = ['razer_shopeepay', 'shopee_pay'].
• One /payment_methods/ call + one static cache serves both groups.
• dnqr: prefer dnqr, drop duitnow_qr. shopee: prefer shopee_pay, drop razer_shopeepay.
• Short-circuits (no API) when neither group is configured; falls back to expanded whitelist on API failure.
• Comma-string setting + validation unchanged; no separate selectable shopee option added.

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Shopee Pay → shopee_pay (modern) with backward-compatible migration

Merchant dashboard now stores shopee_pay instead of razer_shopeepay.

Changes (PluginChip.php):

• Description: whitelist field now recommends shopee_pay; razer_shopeepay noted as legacy (auto-migrated).
• Validation allow-list: accepts shopee_pay (keeps razer_shopeepay).
• In-memory migration: if whitelist contains razer_shopeepay and not shopee_pay, it is replaced with shopee_pay before the resolver runs.
• Resolver: preferred key for the Shopee group changed from shopee to shopee_pay so the modern method wins when both are available (previously the preference check never matched, so both could be emitted). SHOPEE_GROUP constant unchanged. DuitNow QR untouched.

Potential Risks & Review Items

• Resolver preference fix: the preferred key was shopee (never a member), so the priority branch was dead code — both Shopee methods could be emitted. Now shopee_pay is preferred. Confirm this matches intended behavior.
• Migration is in-memory only: stored dashboard value is not rewritten; migration re-runs on every payment. No DB write, so no persistence risk, but the stored value stays razer_shopeepay until manually updated.
• Backward compat: merchants with razer_shopeepay still work (migrated at runtime); merchants with shopee_pay unaffected.
• No DuitNow QR changes — duitnow_qr/dnqr group untouched.