Adds a repo_update tool exposing PATCH /api/v1/repos/{owner}/{name}
with optional pointer fields (archived, description, private,
website, template). Only fields set by the caller are sent on the
wire, so the server patches exactly what was asked for.
Originally needed to archive ingestion-svc cleanly instead of
leaving a README tombstone, and to flip template-go-{agent,web}
to template=true so create_project_from_template stops failing
the "is not marked as template" guard.
Wire-level enforcement of "at least one field" returns ErrValidation
before any network call, preventing no-op PATCHes.
private=false (making a repo public) is allowed but flagged in the
tool description with a "verify intent before calling" warning.
The earlier issue draft suggested an ntfy confirmation hook for
that path — out of scope for this PR; the warning string is the
minimum that fits inside the tool surface today.
Wires NewRepoUpdate into cmd/gitea-mcp/main.go alongside the rest
of the repo_* family.
Closes#12
repo_create: POST /user/repos or /orgs/{org}/repos, is_org flag routes
repo_update: PATCH /repos/{owner}/{repo}, confirm required when private=false
repo_mirror_push: add/list/delete push mirrors, password never returned
