feat: add source_provider mapping for actual VPS provisioning

- Update PricingWithProvider type with source_provider and source_region_code
- Update getPricingWithProvider query to JOIN instance_types for actual plan_id
- Use source_provider (linode/vultr) instead of provider_name (Anvil)
- Use source_region_code for actual provider region (ap-northeast, nrt, icn)

Mapping: anvil_regions.source_provider + anvil_pricing.source_instance_id
         → instance_types.instance_id (actual Linode/Vultr plan)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/repositories/ProvisioningRepository.ts

@@ -196,18 +196,25 @@ export class ProvisioningRepository {
            ap.id as pricing_id,
            0 as provider_id,
            'Anvil' as provider_name,
-           'https://api.anvil.cloud' as api_base_url,
-           ai.name as instance_id,
+           CASE ar.source_provider
+             WHEN 'linode' THEN 'https://api.linode.com/v4'
+             WHEN 'vultr' THEN 'https://api.vultr.com/v2'
+             ELSE 'https://api.anvil.cloud'
+           END as api_base_url,
+           it.instance_id as instance_id,
            ai.display_name as instance_name,
            ar.name as region_code,
            ar.display_name as region_name,
            ap.monthly_price,
            ai.vcpus as vcpu,
            CAST(ai.memory_gb * 1024 AS INTEGER) as memory_mb,
-           ai.disk_gb as storage_gb
+           ai.disk_gb as storage_gb,
+           ar.source_provider,
+           ar.source_region_code
          FROM anvil_pricing ap
          JOIN anvil_instances ai ON ap.anvil_instance_id = ai.id
          JOIN anvil_regions ar ON ap.anvil_region_id = ar.id
+         JOIN instance_types it ON ap.source_instance_id = it.id
          WHERE ap.id = ? AND ai.active = 1 AND ar.active = 1`
       )
       .bind(pricingId)