ci(deploy): mount postgres init as a DIRECTORY (fix 'Is a directory')

The single-file bind mount ./scripts/init-db.sh left a stale empty dir in the
reused act_runner workspace → mounted as a directory → migrations never ran →
empty schemas → backend 28P01/connection failures. Move the init script to
deploy/postgres-initdb/00-init.sh and mount the whole DIR at
/docker-entrypoint-initdb.d (robust, like the migrations dir). Deploy checkout
now 'git clean -ffd' to purge stale workspace dirs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deploy/postgres-initdb/00-init.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# FlatRender V2 — run all schema migrations in order on first postgres init.
+# This whole directory is mounted at /docker-entrypoint-initdb.d (a DIRECTORY mount
+# is robust; a single-file bind mount can leave a stale empty dir in a reused CI
+# workspace → "Is a directory"). Migrations dir mounted read-only at /migrations.
+set -e
+
+MIGRATIONS_DIR="/migrations"
+
+echo "==> FlatRender: running schema migrations from $MIGRATIONS_DIR"
+
+for f in $(ls "$MIGRATIONS_DIR"/*.sql | sort); do
+    echo "  Applying: $(basename "$f")"
+    psql -v ON_ERROR_STOP=1 \
+         --username "$POSTGRES_USER" \
+         --dbname   "$POSTGRES_DB" \
+         --file     "$f"
+done
+
+echo "==> FlatRender: all migrations applied."