TerdutTeam: mint and surface a real invite link (spec.invite)

The actual fix for the human-onboarding gap niklas/terdut-server#23 found --
not a terdut-server change at all. A team-scoped credential is already
owner-equivalent for POST/GET/DELETE /api/teams/{teamID}/invites
(requireTeamOwner's synthetic-membership mechanism, ratified not
accidental per that repo's SERVICE-ACCOUNTS.md), and invite redemption
bypasses signup_mode entirely -- this TerdutTeam controller just never
grew a feature to use either fact.

New spec.invite{enabled, role (member|owner, default member), maxUses
(1-100, default 1)} and status.inviteSecretRef. The Secret lives in the
TerdutTeam's OWN namespace, not the operator's: unlike
status.credentialsSecretRef (a durable, high-privilege credential, kept
operator-side per DESIGN.md §6), an invite is bounded and limited-use,
meant for this namespace's own human operators to read and hand out --
same precedent as TerdutAlertSource's status.webhookURLSecretRef, same-
namespace and OwnerReference'd so deleting the TerdutTeam garbage-collects
it automatically.

internal/controller/terdutteam_invite.go: mints on first spec.invite.enabled,
refreshes a day ahead of terdut-server's fixed 7-day TTL (reading the
Secret's own stored expiresAt, no extra server round-trip per reconcile),
revokes server-side and deletes the Secret when flipped back to false. A
lost invite Secret is silently re-minted rather than treated as
unrecoverable the way TerdutAlertSource's webhook key is -- nothing
external holds a durable dependency on one specific invite link staying
stable, it's read once by one human and handed out.

New tdclient.Invite/CreateInvite/RevokeInvite. New envtest coverage: mint
into the team's own namespace, refresh-before-expiry, revoke-on-disable
(internal/controller/terdutteam_controller_test.go's new "spec.invite"
Describe block), plus the fake server growing invite support
(terdutserver_controller_test.go) -- its handleTeamSubPath dispatcher was
split further (deadman switches into their own handleDeadmanSubPath,
matching the existing handleIntegrationSubPath precedent) to stay under
golangci-lint's gocyclo threshold with the new route added.

examples/demo updated to prove this end to end: 02-team-platform.yaml
turns on spec.invite; run-demo.sh's bootstrap_login/join_demo_teams (the
psql signup_mode flip + a direct team_members INSERT) are replaced by
redeem_platform_invite (reads status.inviteSecretRef, a real POST
/api/signup with the invite token) and join_payments_team (POST
/api/teams/{teamID}/members using Payments' own credential and alice's
user id resolved via GET /api/users, deliberately not given its own
spec.invite, so the demo shows both onboarding paths this feature
unlocks) -- zero kubectl exec/psql calls remain anywhere in the script.
README.md's "First login" section rewritten to match; it no longer
documents the admin-token curl call that 403s against current
terdut-server (niklas/terdut-server#23).

Depends on niklas/terdut-server#24 (the callerMayManageServiceAccount fix
for terdut-operator#3) being released before this is deployed for real --
not required to build or test this change itself, since the envtest fake
never modeled that authorization gap to begin with.

api/v1alpha1/zz_generated.deepcopy.go

@@ -834,6 +834,21 @@ func (in *TerdutTeam) DeepCopyObject() runtime.Object {
 	return nil
 }
 
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *TerdutTeamInvite) DeepCopyInto(out *TerdutTeamInvite) {
+	*out = *in
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new TerdutTeamInvite.
+func (in *TerdutTeamInvite) DeepCopy() *TerdutTeamInvite {
+	if in == nil {
+		return nil
+	}
+	out := new(TerdutTeamInvite)
+	in.DeepCopyInto(out)
+	return out
+}
+
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *TerdutTeamList) DeepCopyInto(out *TerdutTeamList) {
 	*out = *in
@@ -901,6 +916,7 @@ func (in *TerdutTeamSpec) DeepCopyInto(out *TerdutTeamSpec) {
 	*out = *in
 	out.ServerRef = in.ServerRef
 	out.OIDC = in.OIDC
+	out.Invite = in.Invite
 }
 
 // DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new TerdutTeamSpec.
@@ -928,6 +944,11 @@ func (in *TerdutTeamStatus) DeepCopyInto(out *TerdutTeamStatus) {
 		*out = new(SecretKeyRef)
 		**out = **in
 	}
+	if in.InviteSecretRef != nil {
+		in, out := &in.InviteSecretRef, &out.InviteSecretRef
+		*out = new(LocalSecretRef)
+		**out = **in
+	}
 }
 
 // DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new TerdutTeamStatus.