Add pg_dump/pg_restore backup and restore scripts

For moving this project to a new server: git tracks code, not the
Postgres data directory, and raw volume/data-dir copying is fragile
across Postgres versions or architectures (this repo already hit a
collation-version mismatch once from just changing the Postgres
image). pg_dump/pg_restore is the portable way to move the actual
data instead.

scripts/backup-db.sh dumps the running postgres container's database
in pg_dump's custom format into ./backups/ (gitignored — dumps
contain real user data and don't belong in git history). It reads
POSTGRES_USER/POSTGRES_DB from the container's own environment rather
than re-parsing .env, so it can't drift out of sync with the actual
running config.

scripts/restore-db.sh restores a dump into the running container
(--clean --if-exists --single-transaction, so a failure rolls back
atomically instead of leaving a half-restored database), with a
confirmation prompt since it's destructive, skippable via -y.

Added .gitattributes forcing LF on *.sh — Windows git would otherwise
check these out as CRLF, breaking the bash shebang on the Linux
server they're meant to run on.

Verified end to end: took a real backup of the live database, restored
it back over itself, and confirmed exact row-count matches across every
table plus that pgvector similarity search still works on the restored
embeddings (not just that the bytes round-tripped).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/restore-db.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Restores a dump produced by backup-db.sh into the running "postgres" container.
+# Destructive: drops and recreates every object in the target database before restoring.
+#
+# Usage: scripts/restore-db.sh path/to/dnd_backup_20260101_120000.dump [-y]
+#   -y   skip the confirmation prompt (for non-interactive/scripted use)
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+skip_confirm=false
+file=""
+for arg in "$@"; do
+  if [ "$arg" = "-y" ]; then
+    skip_confirm=true
+  else
+    file="$arg"
+  fi
+done
+
+if [ -z "$file" ]; then
+  echo "Usage: $0 path/to/backup.dump [-y]" >&2
+  exit 1
+fi
+if [ ! -f "$file" ]; then
+  echo "Error: file not found: $file" >&2
+  exit 1
+fi
+
+if [ "$skip_confirm" = false ]; then
+  read -r -p "This will DROP and recreate every table in the target database. Continue? [y/N] " reply
+  case "$reply" in
+    [yY]|[yY][eE][sS]) ;;
+    *) echo "Aborted."; exit 1 ;;
+  esac
+fi
+
+echo "Restoring ${file} ..."
+docker compose exec -T postgres sh -c \
+  'pg_restore -U "$POSTGRES_USER" -d "$POSTGRES_DB" --clean --if-exists --no-owner --no-privileges --single-transaction' \
+  < "$file"
+
+echo "Done."