feat: add container snapshot and SDN subnet cmdlets

Container snapshots (4 cmdlets):
- Get-PveContainerSnapshot, New-PveContainerSnapshot
- Remove-PveContainerSnapshot, Restore-PveContainerSnapshot
- Service methods in ContainerService
- Pester unit tests

SDN subnet management (3 cmdlets):
- Get-PveSdnSubnet, New-PveSdnSubnet, Remove-PveSdnSubnet
- PveSdnSubnet model and NetworkService methods
- Pester unit tests

Also updates manifest (73 cmdlets), README cmdlet reference, and CHANGELOG.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Conventional Commits](https://www.conventionalcommi
 
 ## [Unreleased]
 
+## [0.1.0-preview] - 2026-03-19
+
 ### Added
 
 - Initial project structure and solution setup
@@ -14,9 +16,10 @@ and this project adheres to [Conventional Commits](https://www.conventionalcommi
 - HTTP client with manual multipart ISO upload (bugzilla 7389 workaround)
 - Typed response models for PVE 8.x and 9.x API resources
 - Service layer for all resource domains
-- PowerShell cmdlets for all supported operations
+- 66 PowerShell cmdlets for VMs, containers, storage, networking, SDN, users, roles, permissions, API tokens, templates, cloud-init, snapshots, and tasks
+- QEMU guest agent cmdlets (Test-PveVmGuestAgent, Get-PveVmGuestNetwork, Invoke-PveVmGuestExec)
 - xUnit unit tests for core library
-- Pester 5 cmdlet tests across OS/PS version matrix
-- Integration test stubs for future live target testing
-- GitHub Actions CI/CD workflows
+- Pester 5 cmdlet tests across OS/PS version matrix (Windows PS 5.1, PS 7.5 on Windows/Linux/macOS)
+- Integration tests against live PVE 8 and PVE 9 instances via Terraform-provisioned nested VMs
+- GitHub Actions CI/CD workflows (build, unit tests, integration tests)
 - Format definitions for default table output on all PS versions