chore: genericize environment-specific examples and fixtures

[atbagan]

Why

Examples, golden fixtures and architecture notes carried identifiers from the environment they were originally recorded against. The categories involved were host names, an internal address range, repository paths, and cluster and tenant names. None of it is needed to understand or exercise the behaviour, and none of it belongs in a public repository.

What

A single consistent fictional namespace throughout:

Category	Now uses
Git host examples	gitlab.example.com, gitlab.internal.example.net
Service host examples	*.example.com
Addresses	RFC 5737 documentation range (192.0.2.0/24)
Repository paths	example-group/<domain>/<service>/live-infrastructure
Cluster names	mgmt-cluster-01, example-tenant

Fixture directories are renamed to describe what they exercise rather than where they came from:

• mature-tenant-prd is the full inventory tenant: helm matched and unmatched mix, native CRs, all three native tiers, base and env split, Flux ownership filter.
• fresh-tenant-dev is the fresh bootstrap shape: the conditional infra-configs gate and the minimal tenant overlay.

Recorded credential material in the fixtures is replaced with deterministic synthetic values of the same shape and length, so the layout engine sees the same structure.

How the goldens were changed

Regenerated with cmd/gitops-fixture-dump, the documented path, rather than edited by hand. The result was then diffed against the previous trees with the identifier substitutions applied: same file set, same content, zero deltas beyond the identifiers themselves (24 and 42 files respectively).

Behaviour

None. The only changes to non-test source are two comments. Regression coverage is untouched:

• Provider URL handling across public GitHub, GitHub Enterprise, GitLab SaaS and self hosted GitLab
• Nested group path preservation and the project ID round trip
• Provider host mismatch refusal
• Repository pagination across the full range of page boundaries, including the mid walk failure case
• Layout and coverage goldens

Full suite, build and vet pass. Two files remain unformatted by gofmt; both were already unformatted on main and are deliberately not touched here to keep this change to one purpose.