feat: add restore drill coverage

Add restore verification and image-storage recovery scripts, update deployment documentation, and note the restore drill milestone in the implementation status.

scripts/restore-postgres.test.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+set -eu
+
+script_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+test_dir=$(mktemp -d)
+trap 'rm -rf "$test_dir"' EXIT
+mkdir -p "$test_dir/bin"
+
+printf '%s\n' '#!/bin/sh' 'exit 0' > "$test_dir/bin/docker"
+chmod +x "$test_dir/bin/docker"
+
+printf '%s\n' 'fake dump' > "$test_dir/backup.dump"
+PATH="$test_dir/bin:$PATH" \
+  BACKUP_FILE="$test_dir/backup.dump" \
+  POSTGRES_DB=inventory \
+  POSTGRES_USER=inventory \
+  POSTGRES_PASSWORD=secret \
+  sh "$script_dir/restore-postgres.sh" >/dev/null
+
+if BACKUP_FILE="$test_dir/empty.dump" \
+  POSTGRES_DB=inventory \
+  POSTGRES_USER=inventory \
+  POSTGRES_PASSWORD=secret \
+  sh "$script_dir/restore-postgres.sh" >/dev/null 2>&1; then
+  printf '%s\n' 'Expected empty backup to fail.' >&2
+  exit 1
+fi
+
+if BACKUP_FILE="$test_dir/missing.dump" \
+  POSTGRES_DB=inventory \
+  POSTGRES_USER=inventory \
+  POSTGRES_PASSWORD=secret \
+  sh "$script_dir/restore-postgres.sh" >/dev/null 2>&1; then
+  printf '%s\n' 'Expected missing backup to fail.' >&2
+  exit 1
+fi
+
+printf '%s\n' 'restore-postgres tests passed.'