Create a managed NFS or SMB file share

Provisions a new managed file share in the active scope from the file share creation form. The caller picks a share name (used in the mount path / UNC name), a protocol (NFS 4.1 or SMB 3.1.1 — SMB additionally binds to an Active Directory domain), a performance tier (Standard/Premium/Burst), the provisioned size in GB, the virtual network in which mount targets are created, encryption-at-rest, and governance tags. On acceptance the share is created in status CREATING with its mount targets allocated in the chosen network, and it becomes discoverable in the scoped file-share list. Billing is for provisioned capacity per hour at the region's file-share storage rate per GB-month (one rate for every tier); pricePerGbMonthlyCents is a fixed per-tier figure in hundredths of the currency unit, not the rate billing charges. Validation: name must match ^[a-z0-9][a-z0-9-]{1,61}[a-z0-9]$ (3–63 chars, lowercase letters, digits, hyphens) and be unique within the scope (duplicate → 409 CONFLICT); provisionedGb ≥ 100; protocol one of NFS|SMB; tier one of Standard|Premium|Burst; network must reference a virtual network the caller can use; adDomain is required when protocol=SMB and must be null for NFS — any violation → 422 VALIDATION_ERROR. Scope quota for file-share capacity is enforced (→ 409 QUOTA_EXCEEDED); zonal capacity for the tier is checked (→ 409 CAPACITY_UNAVAILABLE). RBAC: owner|admin|contributor. Async & state: Asynchronous; returns 202 with the full FileShare resource in its transitional CREATING state. Terminal states: AVAILABLE on success, ERROR on provisioning failure. Progress is emitted as resource.updated SSE frames with kind "storage.file_share" patching status, mountTargets and updatedAt. Errors: 401 unauthenticated; 403 insufficient role; 404 unknown scopeId or referenced network; 409 CONFLICT duplicate share name; 409 QUOTA_EXCEEDED scope capacity quota; 409 CAPACITY_UNAVAILABLE no tier capacity in the region; 422 invalid field values; 429 rate limited; 500 unexpected failure. Idempotency/Concurrency: Idempotency-Key is required; replaying the same key returns the original 202 response (same share id) without provisioning a second share.