Epic: Provisioning simulator

[CodeBuildder]

Epic — tracking issue. Children:

• Volume API (create/attach/detach/delete) + state machine #19
• VLAN-subnet API (create/delete + CIDR alloc) #20
• Instance API (provision/terminate + lifecycle states) #21
• Per-endpoint fault hooks (latency/error/partial/quota injection) #22
• OpenAPI spec + health/metrics endpoints #23