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.

internal/controller/terdutserver_controller_test.go

@@ -9,6 +9,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -35,6 +36,11 @@ import (
 const (
 	fakeVersionString = "test"
 	errJSONKey        = "error"
+	// deadmanSwitchesPath is the literal path (not Printf'd like the others
+	// below) shared by the exact-match collection route and the dispatcher
+	// that routes into it -- goconst flags three occurrences of the same
+	// string, so this is that string, once.
+	deadmanSwitchesPath = "/deadman/switches"
 )
 
 // fakeTerdutServer reproduces the exact stateful semantics of
@@ -83,6 +89,14 @@ type fakeTerdutServer struct {
 	nextIntegrationID int64
 	integrations      map[int64]map[int64]tdclient.Integration // teamID -> integrationID -> integration
 	integrationDelete map[int64]bool                           // integrationID -> true once DELETEd, for 404-on-redelete
+
+	// invites/nextInviteID/inviteDelete back TerdutTeam's own invite-minting
+	// feature -- no unique constraint on an invite server-side either (every
+	// POST mints a brand new row, confirmed against source), same keyed-by-id
+	// shape as switches/integrations.
+	nextInviteID int64
+	invites      map[int64]map[int64]tdclient.Invite // teamID -> inviteID -> invite
+	inviteDelete map[int64]bool                      // inviteID -> true once DELETEd, for 404-on-redelete
 }
 
 func newFakeTerdutServer() (*fakeTerdutServer, *httptest.Server) {
@@ -100,6 +114,9 @@ func newFakeTerdutServer() (*fakeTerdutServer, *httptest.Server) {
 
 		integrations:      map[int64]map[int64]tdclient.Integration{},
 		integrationDelete: map[int64]bool{},
+
+		invites:      map[int64]map[int64]tdclient.Invite{},
+		inviteDelete: map[int64]bool{},
 	}
 	return f, httptest.NewServer(f)
 }
@@ -265,7 +282,26 @@ func (f *fakeTerdutServer) handleTeamSubPath(w http.ResponseWriter, r *http.Requ
 		f.escalation[id] = req
 		w.WriteHeader(http.StatusNoContent)
 
-	case rest == "/deadman/switches" && r.Method == http.MethodGet:
+	case rest == deadmanSwitchesPath || strings.HasPrefix(rest, deadmanSwitchesPath+"/"):
+		f.handleDeadmanSubPath(w, r, id, rest)
+
+	case rest == "/integrations" || strings.HasPrefix(rest, "/integrations/"):
+		f.handleIntegrationSubPath(w, r, id, rest)
+
+	case rest == "/invites" || strings.HasPrefix(rest, "/invites/"):
+		f.handleInviteSubPath(w, r, id, rest)
+
+	default:
+		w.WriteHeader(http.StatusNotFound)
+	}
+}
+
+// handleDeadmanSubPath answers GET/POST /api/teams/{id}/deadman/switches and
+// PUT/DELETE .../deadman/switches/{switchID} -- split out of
+// handleTeamSubPath for the same gocyclo reason as handleIntegrationSubPath.
+func (f *fakeTerdutServer) handleDeadmanSubPath(w http.ResponseWriter, r *http.Request, id int64, rest string) {
+	switch {
+	case rest == deadmanSwitchesPath && r.Method == http.MethodGet:
 		existing := f.switches[id]
 		out := make([]tdclient.DeadmanSwitch, 0, len(existing))
 		for _, s := range existing {
@@ -273,7 +309,7 @@ func (f *fakeTerdutServer) handleTeamSubPath(w http.ResponseWriter, r *http.Requ
 		}
 		writeJSON(w, http.StatusOK, out)
 
-	case rest == "/deadman/switches" && r.Method == http.MethodPost:
+	case rest == deadmanSwitchesPath && r.Method == http.MethodPost:
 		var req deadmanSwitchFakeRequest
 		_ = json.NewDecoder(r.Body).Decode(&req)
 		f.nextSwitchID++
@@ -328,8 +364,48 @@ func (f *fakeTerdutServer) handleTeamSubPath(w http.ResponseWriter, r *http.Requ
 		f.switchDelete[switchID] = true
 		w.WriteHeader(http.StatusNoContent)
 
-	case rest == "/integrations" || strings.HasPrefix(rest, "/integrations/"):
-		f.handleIntegrationSubPath(w, r, id, rest)
+	default:
+		w.WriteHeader(http.StatusNotFound)
+	}
+}
+
+// handleInviteSubPath answers POST /api/teams/{id}/invites and
+// DELETE .../invites/{inviteID} -- split out for the same gocyclo reason as
+// handleIntegrationSubPath.
+func (f *fakeTerdutServer) handleInviteSubPath(w http.ResponseWriter, r *http.Request, id int64, rest string) {
+	switch {
+	case rest == "/invites" && r.Method == http.MethodPost:
+		var req struct {
+			Role    string `json:"role"`
+			MaxUses int64  `json:"max_uses"`
+		}
+		_ = json.NewDecoder(r.Body).Decode(&req)
+		f.nextInviteID++
+		inviteID := f.nextInviteID
+		inv := tdclient.Invite{
+			ID: inviteID, TeamID: id, Role: req.Role, MaxUses: req.MaxUses,
+			ExpiresAt: time.Now().Add(7 * 24 * time.Hour),
+			URL:       fmt.Sprintf("https://terdut.example.invalid/signup?invite=invite-token-%d", inviteID),
+		}
+		if f.invites[id] == nil {
+			f.invites[id] = map[int64]tdclient.Invite{}
+		}
+		f.invites[id][inviteID] = inv
+		writeJSON(w, http.StatusCreated, inv)
+
+	case strings.HasPrefix(rest, "/invites/") && r.Method == http.MethodDelete:
+		inviteID, ok := parseTrailingID(rest, "/invites/")
+		if !ok {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if _, exists := f.invites[id][inviteID]; !exists {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		delete(f.invites[id], inviteID)
+		f.inviteDelete[inviteID] = true
+		w.WriteHeader(http.StatusNoContent)
 
 	default:
 		w.WriteHeader(http.StatusNotFound)