fix(infra): wait for postgres readiness before running migrations on container start

Installs postgresql-client in the dev image so pg_isready is available.
The startup script now polls until postgres accepts connections, preventing
the P1001 "can't reach database" crash when the app container starts before
postgres is fully ready.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tooling/docker/app-dev-start.sh

@@ -1,6 +1,13 @@
 #!/bin/sh
 set -eu
 
+# Wait for postgres to be ready before running migrations
+echo "Waiting for postgres..."
+until pg_isready -h "${POSTGRES_HOST:-postgres}" -p "${POSTGRES_PORT:-5432}" -q; do
+  sleep 1
+done
+echo "Postgres is ready."
+
 # Regenerate Prisma client (needed after bind-mount overlays the image layer)
 pnpm --filter @capakraken/db db:generate