Add public service-layer wrapper for modifyZones in CloudKitService

[leogdion]

Context

Sources/MistKit/Generated/Client.swift:1766 exposes internal func modifyZones(_ input: Operations.modifyZones.Input) async throws -> Operations.modifyZones.Output from the generated layer, but there is no public CloudKitService wrapper.

The sibling zone operations are wrapped in Sources/MistKit/Service/Extensions/CloudKitService+ZoneOperations.swift:

• public func listZones(database:) async throws(CloudKitError) -> [ZoneInfo]
• public func lookupZones(zoneIDs:database:) async throws(CloudKitError) -> [ZoneInfo]

modifyZones has no equivalent, which means external consumers (including MistDemo's planned modify-zones command in #215) cannot reach the endpoint at all.

Scope

Add a public func modifyZones(...) method to CloudKitService+ZoneOperations.swift that:

• Takes ergonomic Swift inputs (e.g. an [ZoneOperation] describing create / delete with ZoneIDs) instead of raw Operations.modifyZones.Input.
• Returns ergonomic Swift outputs (e.g. [ZoneInfo] or a small ZoneModifyResult value type) instead of Operations.modifyZones.Output.
• Declares throws(CloudKitError) and routes failures through mapToCloudKitError(_:context:).
• Resolves auth + transport via self.client(for: database) — modifyZones is private/shared-database only, so reject .public with a clear error.
• Validates inputs (non-empty operations list, non-empty zone names) before hitting the network, mirroring the guards in lookupZones.
• Normalizes the response via responseProcessor if a matching helper exists; otherwise add one alongside the listZones/lookupZones processors.

Tests

• Unit tests in Tests/MistKitTests/Service/ covering: create-only batch, delete-only batch, mixed batch, empty-operations rejection, empty-zone-name rejection, .public rejection, error mapping.
• Mock client coverage following the pattern used for listZones / lookupZones.

Out of scope

• The MistDemo modify-zones command itself — that stays in Phase 4: Advanced Operations - MistDemo #215 and depends on this issue.

Definition of Done

• public func modifyZones(...) lands in CloudKitService+ZoneOperations.swift
• Generated-layer call is encapsulated; no caller has to touch Operations.modifyZones.*
• Unit tests cover create, delete, mixed, validation, and error paths
• CLAUDE.md "CloudKitService Operations" table updated to list modifyZones
• swift build + swift test + ./Scripts/lint.sh clean

Related

• Parent: Phase 4: Advanced Operations - MistDemo #215 (MistDemo modify-zones command depends on this)