feat(databases): backup import — upload .tar.gz as a restore point

D5. POST /databases/:id/backups/import accepts a gzipped tar archive
(multipart `file` field or raw application/gzip body, 2 GiB ceiling),
stages it to a temp file, streams it into the backup volume via the
started holder container, and registers a completed backup row — a
first-class restore point that also ships offsite when a target is
assigned. External databases rejected.

Also fixes `containr databases restore` — it never sent database_id,
which the API requires, so every CLI restore failed validation.

CLI: databases import-backup <id> <file|-> (stdin support via new
client.DoRaw). UI: Import button in the backups row. OpenAPI + docs.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/lib/api-client.ts

@@ -1727,6 +1727,21 @@ export async function restoreDatabaseBackup(id: string, backupId: string): Promi
   });
 }
 
+export async function importDatabaseBackup(id: string, file: File): Promise<{ backup_id: string; size: string }> {
+  const form = new FormData();
+  form.append('file', file);
+  const resp = await fetch(`${getApiBaseUrl()}/databases/${encodeURIComponent(id)}/backups/import`, {
+    method: 'POST',
+    headers: authHeaders(),
+    body: form,
+  });
+  const payload = await resp.json().catch(() => ({}));
+  if (!resp.ok) {
+    throw new ApiError(payload.error || 'Import failed', resp.status);
+  }
+  return payload;
+}
+
 export async function createManagedDatabase(
   input: CreateDatabaseInput,
 ): Promise<{ id: string; status: string }> {