chore(asset): add postgres bootstrap and pg_ident template

Idempotent SQL for role and database creation, split between the
postgres-database scope (bootstrap.sql) and the moments-database
scope (bootstrap-moments.sql), since CREATE DATABASE can't run
inside a DO block or transaction.

Roles:
  moments_rw — owner of the moments database; runs migrations
               and writes events from moments-worker.
  moments_ro — read-only; consumed by moments-api.

The pg_ident template is rendered per-host by deploy.sh once it
lands; one (host, role) mapping per file. Reload required on both
magrathea and frankie after install — pg_ident is not replicated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

asset/sql/bootstrap-moments.sql

@@ -0,0 +1,17 @@
+-- In-database grants for the moments database.
+-- Run after asset/sql/bootstrap.sql, against the moments database.
+-- Idempotent — safe to re-run on every deploy.
+--
+--   psql -h magrathea.kosherinata.internal -U postgres -d moments \
+--        -f asset/sql/bootstrap-moments.sql
+--
+-- The schema itself is created by sqlx migrations executed by moments-api
+-- on startup (which runs as moments_rw, the database owner). This file
+-- only manages the read-only role's access to whatever moments_rw creates.
+
+GRANT USAGE ON SCHEMA public TO moments_ro;
+GRANT SELECT ON ALL TABLES IN SCHEMA public TO moments_ro;
+
+-- Tables created later by moments_rw (running migrations) inherit SELECT for moments_ro.
+ALTER DEFAULT PRIVILEGES FOR ROLE moments_rw IN SCHEMA public
+  GRANT SELECT ON TABLES TO moments_ro;

asset/sql/bootstrap.sql

@@ -0,0 +1,26 @@
+-- moments role and database bootstrap.
+-- Run as a postgres superuser against the cluster's `postgres` database.
+-- Idempotent — safe to re-run on every deploy.
+--
+--   psql -h magrathea.kosherinata.internal -U postgres -d postgres \
+--        -f asset/sql/bootstrap.sql
+--
+-- After this completes, run asset/sql/bootstrap-moments.sql against the
+-- newly created `moments` database to apply the in-database grants.
+
+DO $$
+BEGIN
+  IF NOT EXISTS (SELECT FROM pg_roles WHERE rolname = 'moments_rw') THEN
+    CREATE ROLE moments_rw LOGIN;
+  END IF;
+  IF NOT EXISTS (SELECT FROM pg_roles WHERE rolname = 'moments_ro') THEN
+    CREATE ROLE moments_ro LOGIN;
+  END IF;
+END
+$$;
+
+SELECT 'CREATE DATABASE moments OWNER moments_rw'
+WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'moments')
+\gexec
+
+GRANT CONNECT ON DATABASE moments TO moments_ro, moments_rw;