feat(fase-13): server_admins + admin_actions audit log model

Migration 024 introduces the orthogonal global role and the append-only
audit log. server_admins is a separate table (not a column on users) so
that promote/revoke don't require a JWT re-issue; is_server_admin() is a
STABLE SECURITY DEFINER helper matching the shape of is_admin/is_member.

admin_actions has only a SELECT policy (admin-only) — no INSERT/UPDATE/
DELETE policies, so only the SECURITY DEFINER RPCs in migration 025 can
write to it. actor_id FK uses RESTRICT so the audit trail outlives
admins.

Bootstrap via infra/db-init/10-server-admin-seed.sh on first volume
init (reads SERVER_ADMIN_EMAIL); supabase/seed.sql also pre-seeds Ana
for dev/test because docker-entrypoint-initdb.d does not re-fire on
long-lived dev volumes. Documented in .env.erosi.example.

20 new pgTAP assertions cover schema shape, RLS posture, FK behaviour,
and the SECURITY DEFINER + STABLE attributes on is_server_admin().

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

infra/db-init/10-server-admin-seed.sh

@@ -0,0 +1,70 @@
+#!/bin/bash
+# Fase 13.1.2 — server admin bootstrap.
+#
+# Runs once on first volume init (docker-entrypoint-initdb.d). Reads
+# SERVER_ADMIN_EMAIL from the environment. If the env var is set AND the
+# `public.server_admins` table is empty AND there's a matching `public.users`
+# row, promotes that user to server admin.
+#
+# Idempotent + safe to re-run:
+#   * If SERVER_ADMIN_EMAIL is unset → no-op (logged).
+#   * If the table already has at least one admin → no-op (logged). This is the
+#     guard the plan calls "second invocation with a different email shouldn't
+#     touch previous rows".
+#   * If the email is set but no matching user exists yet (first prod boot:
+#     volume is fresh, nobody has signed in via Keycloak yet) → log a warning
+#     and exit cleanly. The operator must re-run this script (or insert
+#     manually) after the first login. Documented in docs/deployment.md.
+#
+# Order: the leading digit (10-) puts this AFTER 00-role-passwords.sh so all
+# the supporting role + schema bootstrap has happened.
+#
+# Caveat: `docker-entrypoint-initdb.d` only fires on a FRESH volume. On a
+# long-lived dev volume it never runs again after the first init. We rely on
+# supabase/seed.sql to also insert the seed dev admin (Ana) so the integration
+# + e2e suites have a deterministic admin without depending on initdb timing.
+
+set -e
+
+if [ -z "${SERVER_ADMIN_EMAIL:-}" ]; then
+    echo "==> server-admin-seed: SERVER_ADMIN_EMAIL not set, skipping"
+    exit 0
+fi
+
+echo "==> server-admin-seed: looking up ${SERVER_ADMIN_EMAIL}…"
+
+# Bash expands ${SERVER_ADMIN_EMAIL} inside the unquoted heredoc tag below.
+# The PL/pgSQL `$$ ... $$` dollar-quoting needs to be escaped (\$\$) so bash
+# doesn't try to interpolate it. Same idea as 00-role-passwords.sh.
+psql -v ON_ERROR_STOP=1 --username postgres --dbname postgres <<EOSQL
+    DO \$\$
+    DECLARE
+        v_email      text := '${SERVER_ADMIN_EMAIL}';
+        v_user_id    uuid;
+        v_existing   int;
+    BEGIN
+        SELECT count(*) INTO v_existing FROM public.server_admins;
+        IF v_existing > 0 THEN
+            RAISE NOTICE 'server-admin-seed: server_admins already populated (% row(s)), skipping', v_existing;
+            RETURN;
+        END IF;
+
+        SELECT id INTO v_user_id
+        FROM   public.users
+        WHERE  lower(email) = lower(v_email);
+
+        IF v_user_id IS NULL THEN
+            RAISE WARNING 'server-admin-seed: no public.users row matches email %, skipping (re-run after first login)', v_email;
+            RETURN;
+        END IF;
+
+        INSERT INTO public.server_admins (user_id)
+        VALUES (v_user_id)
+        ON CONFLICT (user_id) DO NOTHING;
+
+        RAISE NOTICE 'server-admin-seed: promoted user % (email %)', v_user_id, v_email;
+    END
+    \$\$;
+EOSQL
+
+echo "==> server-admin-seed: done"