Gitea and Forgejo have no gist or snippet feature at all: gitea.com and
codeberg.org both answer 404 for /api/v1/gists, /snippets and /pastes, and the
SDK carries no service for one.

Unlike Sites, this is not implemented for EITHER source type. Sites is
advertised on the shared type and refuses at runtime, because whether an
instance runs a pages service is configuration. Here there is nothing to
configure, so the type assertion fails outright — the honest answer.

The test stops someone adding a stub that returns ErrNotSupported from every
method, which advertises a capability the forge cannot honour and defeats the
assertion callers branch on.

Compatibility note: requires forge v0.11.0, which introduces forge.Snippets.

Implements spec 0007 D2:
0007 snippets and gists

A handle cannot own or enforce copyright, and the estate was
split between two holder strings. Names both so the notice
identifies a legal person without orphaning the handle.

Migrates to forge v0.12.0, whose ProviderFactory takes an Endpoint rather
than a ReleaseSourceConfig. Settings.ReleaseSource becomes
Settings.Endpoint, and SettingsFromConfig takes the ROOT configuration
rather than a pre-scoped subtree, resolving its own section from the
endpoint.

Two fields disappear because the endpoint now carries what they held, and
both were duplicates that had to be kept in agreement:

Settings.SourceType existed so diagnostics could say which of this
module's two registrations built the provider. Endpoint.Type is that,
already.

registration.section declared the configuration subtree a source type
resolves from. It was always equal to the source type, and
forge.Endpoint.Section derives the subtree from exactly that string, so
the field was a second place to get the same answer wrong.

The factory now SETS Endpoint.Type from its registration rather than
letting it default downstream. That is load-bearing here rather than
tidiness: one module serves two source types, and a defaulted Type sent a
Codeberg lookup to gitea's configuration section — the exact
cross-authentication spec 0001 settled, reintroduced silently. The section
isolation tests caught it.

TestGiteaProvider_IgnoresAPIVersionParam becomes
TestGiteaProvider_TargetsAPIV1. It guarded that an api_version entry in
Params was inert; the address carries no Params, so there is no longer a
documented-looking key that can be set and quietly do nothing. The
positive assertion — the SDK owns the version segment and targets v1 —
is what remains worth pinning.

Implements forge spec 0008 D1 and D2 for this adapter.