Stage 2: TerdutTeam (create, mint team credential, rename/oidc-groups, delete)

Implements ROADMAP.md Stage 2 against terdut-server's now-real
GET /api/teams?name= (TEAM-LOOKUP.md, landed in terdut-server just
before this commit) -- without it, the adopt-on-409 pattern this
controller depends on for team creation had no server-side lookup to
call, the same gap TerdutServer's own bootstrap flow hit and fixed in
Stage 1.

- api/v1alpha1: TerdutTeamSpec per DESIGN.md §4.2 (serverRef, displayName,
  oidc). status.credentialsSecretRef drops namespace for key, matching
  the fix already applied to TerdutServer's.
- internal/controller:
  - terdutteam_controller.go: resolves serverRef (same-namespace by
    default; cross-namespace gated by the target TerdutServer's
    spec.allowedTeams, DESIGN.md §4.6), waits for that TerdutServer to be
    Bootstrapped (no cross-controller RPC -- reads its
    status.credentialsSecretRef directly, DESIGN.md §5), creates the team
    and mints its team-scoped credential using the TerdutServer's
    instance-scoped one, then applies rename/oidc-groups with the
    team-scoped credential every reconcile (both are idempotent PUTs of
    the whole resource -- applied unconditionally rather than diffed
    against a stored last-applied value, same "cheap because it's small"
    reasoning §5 already gives the escalation policy's whole-policy PUT).
  - terdutteam_allowedteams.go: the §4.6 consent check in isolation from
    any client, unit-tested directly against hand-built inputs.
  - terdutteam_bootstrap.go: create-or-adopt-on-409 for the team itself
    (via TEAM-LOOKUP.md) and for its team-scoped service account (via the
    same GET-by-name+mint-new-key pattern Stage 1 already uses for the
    instance account).
  - secrets.go: extracted TerdutServer's write/read-credential-Secret
    helpers into free functions, now shared by both controllers rather
    than duplicated.
  - Finalizer deletes the team server-side (owner-gated, needs the
    team-scoped credential -- confirmed against source that an
    instance-scoped one does not satisfy requireTeamOwner, same finding
    as TEAM-LOOKUP.md's) and cleans up its credentials Secret. A team
    created but never fully reconciled to Ready (no team-scoped
    credential ever minted) is left orphaned server-side on delete -- a
    known, documented limitation (terdut-server has no delete path that
    doesn't require owner-equivalent access), not a silent gap.
- internal/tdclient: Team type, CreateTeam, GetTeamByName, RenameTeam,
  DeleteTeam, SetTeamOIDCGroups, CreateTeamServiceAccount -- matching
  terdut-server's real handlers' shapes field-for-field, same as Stage
  1's client additions.
- Tests: envtest covering the happy path, both not-ready reasons
  (ServerRefNotFound, WaitingForServer), cross-namespace allow/deny
  (default-closed and explicit All), both adopt-on-409 paths (team
  itself, team-scoped service account), and deletion. Extended the shared
  fakeTerdutServer (Stage 1) with team endpoints rather than writing a
  second, separately-drifting fake. 72.8%/30.6% coverage, 0 lint issues.

Verified locally: make fmt lint test build all clean.

config/samples/kustomization.yaml

@@ -1,4 +1,5 @@
 ## Append samples of your project ##
 resources:
 - terdut_v1alpha1_terdutserver.yaml
+- terdut_v1alpha1_terdutteam.yaml
 # +kubebuilder:scaffold:manifestskustomizesamples

config/samples/terdut_v1alpha1_terdutteam.yaml

@@ -0,0 +1,20 @@
+apiVersion: terdut.ryuvia.com/v1alpha1
+kind: TerdutTeam
+metadata:
+  labels:
+    app.kubernetes.io/name: terdut-operator
+    app.kubernetes.io/managed-by: kustomize
+  name: terdutteam-sample
+spec:
+  # serverRef.namespace is optional, defaulting to this TerdutTeam's own
+  # namespace (the common case). Set it only to reference a TerdutServer in
+  # a different namespace -- which needs that TerdutServer's own
+  # spec.allowedTeams to admit this namespace (DESIGN.md §4.6), otherwise
+  # this reports Ready: False, reason: RefNotPermitted.
+  serverRef:
+    name: terdutserver-sample
+  displayName: Platform
+  # oidc is optional -- omit entirely for a password-login-only install.
+  # oidc:
+  #   memberGroup: terdut-platform-members
+  #   ownerGroup: terdut-platform-owners