fix: say why backup and restore do not apply to a native install

Both accepted a native install and then drove `docker compose` in a directory
with no compose file, so the user got "no configuration file provided" rather
than an explanation. They now refuse with what to do instead, and restore
refuses before it reads the archive or stops anything.

docsgpt/deploy/commands.py

@@ -568,6 +568,10 @@ def backup(args, context: Optional[Context] = None) -> int:
     env = _installed(directory)
     if env is None:
         return 1
+    if _mode(directory) == "native":
+        raise DeployError(
+            f"{directory} is a native install: its database and its files are not in Docker volumes, so there is nothing here to archive. Back up the PostgreSQL that POSTGRES_URI points at with pg_dump, and copy the indexes, inputs and vectors folders from the data home."
+        )
 
     out_dir = Path(args.out).expanduser() if args.out else directory / "backups"
     taken_at = datetime.now(timezone.utc)
@@ -657,13 +661,17 @@ def _restore_data(context: Context, directory: Path, archive: Path, volumes: lis
 def restore(args, context: Optional[Context] = None) -> int:
     """Put a backup's database and data volumes back over this install."""
     context = context or Context.default(args)
+    directory = stack.stack_dir(args.dir)
+    if _mode(directory) == "native":
+        raise DeployError(
+            f"{directory} is a native install: its database and its files are not in Docker volumes, so there is nothing here to archive. Back up the PostgreSQL that POSTGRES_URI points at with pg_dump, and copy the indexes, inputs and vectors folders from the data home. `docsgpt restore` puts back what `docsgpt backup` wrote for a Docker install."
+        )
     archive = Path(args.archive).expanduser()
     manifest = backup_format.read_manifest(archive)
     backup_format.check_version(manifest, context.version, args.force)
     # Everything the archive declares is checked here, while DocsGPT is still up.
     volumes = backup_format.validate(archive, manifest)
 
-    directory = stack.stack_dir(args.dir)
     env = _installed(directory)
     if env is None:
         return 1