Authenticate with a seeded operator key; fold escalation and switches into TerdutTeam

Credentials: the TerdutServer controller generates <name>-operator-key in
the server's own namespace (owned by it) and hands it to the pods as
TERDUT_OPERATOR_KEY; the server creates its instance-scoped account from it
at every start. A replaced Secret rolls the pods. The bootstrap handshake,
the checkpoint Secret, per-team service accounts and credentials Secrets,
BootstrapStateLost and credentials.deletionPolicy are gone.

CRDs: TerdutServer, TerdutTeam and TerdutAlertSource. TerdutEscalationRule
and TerdutDeadmanSwitch become spec.escalation and spec.deadmanSwitches[]
on the team (matched by name, extras removed); team invites are removed.
A team is created under the identity <namespace>/<name> (external_id), so a
retry, a lost status or a deleted team heal by repeating the same call, and
a display name owned by another team is TeamNameTaken instead of an
adoption. The server resolves escalation usernames (UnknownUser condition).
OIDC claim names and trustEmail are spec fields.

Fixes: query values are URL-escaped; every delete treats 404 as success;
deleting a team no longer depends on allowedTeams consent; a switch or
integration deleted on the server is recreated; unnamed switches take the
CR's name.

Cleanup: scaffold e2e test, AGENTS.md, devcontainer, unused config/ pieces
and Client.Version() removed; DESIGN.md, README, ROADMAP and the demo
(run-demo.sh, manifests) rewritten for the new design. Secret RBAC stays
cluster-wide, now stated in DESIGN.md section 9.

Claude-Session: https://claude.ai/code/session_016mBLURvJoMuUEr9cB2RpUN

examples/demo/03-team-payments.yaml

@@ -6,9 +6,15 @@ spec:
   serverRef:
     name: terdut-operator-demo
   displayName: Payments
-  # No spec.invite here, deliberately: run-demo.sh joins alice to this team
-  # through POST /api/teams/{teamID}/members instead (this team's own
-  # credential, same owner-equivalent reach spec.invite relies on, plus her
-  # user id resolved via GET /api/users), once she already has an account
-  # from Platform's invite -- showing both onboarding paths this feature
-  # unlocks, not just the one.
+  escalation:
+    repeatCount: 1
+    fallbackTopic: payments-fallback
+    levels:
+      - timeout: 5m
+        targets:
+          - kind: oncall
+  deadmanSwitches:
+    - name: payments-watchdog
+      matcher: "alertname=PaymentsWatchdog"
+      timeout: 15m
+      severity: critical