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.

config/crd/bases/terdut.ryuvia.com_terdutteams.yaml

@@ -60,6 +60,47 @@ spec:
                   create rule, via TEAM-LOOKUP.md).
                 minLength: 1
                 type: string
+              invite:
+                description: |-
+                  TerdutTeamInvite requests a standing invite link into this team, minted
+                  with the team's own team-scoped credential — requireTeamOwner already
+                  treats that credential as owner-equivalent for every /invites route
+                  (ratified, not a gap, as of terdut-server's SERVICE-ACCOUNTS.md). This is
+                  the real answer to "how does a human ever get a first login on a
+                  password-only, operator-managed install" (terdut-server#23): no signup_mode
+                  flip, no admin token, just a link redeemed the same way anyone else's
+                  invite would be.
+                properties:
+                  enabled:
+                    description: |-
+                      enabled mints (and keeps refreshed ahead of terdut-server's own fixed
+                      7-day TTL) an invite link while true. Flipping it back to false
+                      revokes the current one server-side rather than leaving it to expire
+                      on its own.
+                    type: boolean
+                  maxUses:
+                    default: 1
+                    description: |-
+                      maxUses bounds how many times this link may be redeemed before it
+                      stops working, mirroring terdut-server's own 1-100 range
+                      (POST /api/teams/{teamID}/invites). Defaults to 1: a link meant for
+                      one specific person, not a standing door.
+                    format: int64
+                    maximum: 100
+                    minimum: 1
+                    type: integer
+                  role:
+                    default: member
+                    description: |-
+                      role is what the invite grants: member or owner. Defaults to member —
+                      owner by default would make every invite link a standing
+                      administrative credential for the team, a much bigger blast radius
+                      than "let a human see the queue".
+                    enum:
+                    - member
+                    - owner
+                    type: string
+                type: object
               oidc:
                 description: |-
                   TerdutTeamOIDC binds which identity-provider groups grant membership and
@@ -168,6 +209,24 @@ spec:
                 - key
                 - name
                 type: object
+              inviteSecretRef:
+                description: |-
+                  inviteSecretRef is this team's current invite link, if spec.invite.enabled.
+                  Unlike credentialsSecretRef, this lives in the TerdutTeam's OWN
+                  namespace, not the operator's: an invite is bounded, limited-use, and
+                  meant for this namespace's own human operators to read and hand out,
+                  not a durable high-privilege credential — same shape as
+                  TerdutAlertSource's status.webhookURLSecretRef, not TerdutServer's
+                  cross-namespace credentialsSecretRef. Nil whenever spec.invite.enabled
+                  is false or unset.
+                properties:
+                  name:
+                    description: name is the Secret's name.
+                    minLength: 1
+                    type: string
+                required:
+                - name
+                type: object
               observedGeneration:
                 format: int64
                 type: integer