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>

scripts/init-db.sh

@@ -1,19 +0,0 @@
-#!/bin/bash
-# FlatRender V2 — run all schema migrations in order on first postgres init.
-# Mounted at: /docker-entrypoint-initdb.d/00-init.sh
-# Migrations dir mounted at: /migrations  (read-only)
-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."