Add configurable node hostnames

[orrious]

Summary

Add an inherited topology hostname property that controls the hostname configured inside a node container.

• inherit hostname from defaults, kinds, groups, or nodes
• default runtime hostname to the topology node ShortName
• propagate the resolved hostname through NodeConfig to Docker and Podman
• treat hostname drift as node recreation during clab apply
• add schema, documentation, release notes, and focused tests

Validation

• full Linux make test suite passed with the Docker runtime available
• golangci-lint v2.12.0: 0 issues
• strict Zensical documentation build: no issues
• macOS/Colima deploy verified configured and runtime hostnames match
• clab apply --dry-run reported config drift: Hostname
• actual apply recreated only the changed node and updated its hostname
• combined integration RPMs were built and installed successfully on linux/amd64 and linux/arm64

This branch is intentionally rebased directly onto upstream main so it contains only the hostname contribution. The separate feature/podman-systemd-support-integration branch retains the previously validated combined build.

[orrious]

Rebased this branch onto current main and force-pushed the updated head.

Current head: 2cb659f5a

Validation completed on the real lab runners:

• x86 runner: go test ./types ./nodes passed
• ARM runner: go test ./types ./nodes passed