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.

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

llms.txt

@@ -24,6 +24,7 @@ Base URL: `https://<host>/api/v1`. OpenAPI: `docs/api/openapi.yaml`.
 - **External databases**: `POST /databases/register-external` (probes first; `{name,type,host,port,database,username,password,ssl}`), `POST /databases/test-connection` (ad-hoc probe → `{ok,latency_ms,error}`), `POST /databases/{id}/test-connection` (re-probe with stored credentials). Rows carry `provider:"external"` + `external{host,port,database,username,has_password,ssl}`; passwords encrypted at rest, never returned. Lifecycle actions and backups reject external rows — no container exists.
 - **Public DB port**: managed databases bind `127.0.0.1` by default; `public_port:true` on create or `PUT /databases/{id} {public_port}` binds `0.0.0.0`. Toggling recreates the container — the data volume persists.
 - **Backup targets**: S3-compatible destinations (`/backup-targets` CRUD + `POST /backup-targets/{id}/test`). Endpoints/buckets are probed before storing; keys encrypted at rest (`has_credentials` only). Assign via `PUT /databases/{id} {backup_target_id}` — empty string clears; external databases reject assignment. Managed backups stay local; a copy ships to `[prefix/]databases/<db-id>/<archive>` and rows expose `remote:true`. Restore prefers the local archive and falls back to the remote object. Deleting a target is refused (409) while databases reference it.
+- **Backup import**: `POST /databases/{id}/backups/import` — upload a `.tar.gz` (multipart `file` or raw `application/gzip` body, ≤2 GiB) to create a restore point; also ships offsite when a target is assigned. CLI: `databases import-backup <id> <file|->`.
 - **Identifiers**: all ids are UUIDs. Tokens: `cnp_` user PATs, `cagt_` agent onboarding tokens.
 
 ## Core objects