Write down the plugin nobody documented, and stop pointing at a deleted branch

PLUGINS.md listed 14 of the 15 bundled plugins. `backups` had no row: the
per-asset configuration backups the collector takes off shopfloor machines,
kind-pluggable, with view and download as separate permissions because a .reg
is a restorable artifact. Added, with the pointer that separates it from
BACKUP-RESTORE.md, which is the database and a different subject.

PLUGIN-LAB-PRINTEDPARTS said the finished implementation lives on branch
feat/printedparts-plugin. That branch was deleted in the v0.8.0 cleanup; only
the 17 lab-stage tags survived, and they are enough. Says so now, and warns
that the tags are a record of contract 0.11-0.13 rather than today's
conventions. Its manifest example carried core_version >=0.12.0 against a
shipped >=0.16.0.

The printer-assignment proposal still said the client script is not built. It
shipped and released, across v0.11.3 and v0.12.0, and the collector half that
contradicted the assigned-vs-observed split was retired in adc7ef4.

PROJECT-MAP regenerated for the test count.

docs/PLUGINS.md

@@ -22,6 +22,7 @@ These plugins are in `plugins/` in this repo. Enable per site with `flask plugin
 | `slides` | Slides for the lobby display and shop-floor screensaver | Upload / reorder / delete per surface. Management gated on the `slides.manage` permission, grantable to non-admin curators; display routes are public. |
 | `tools` | Technician utilities: barcode and QR label generation, unit conversions, Secure Send | Mostly browser-side by design, so an air-gapped bench gets them with no network. Secure Send is the exception and is why this plugin has a blueprint, a table and a migration chain: see [SECURE-SEND.md](SECURE-SEND.md). |
 | `warranty` | Asset warranty tracking | Manual entry now, Dell / Lenovo / HP provider lookups later. Derived coverage status with report buckets. |
+| `backups` | Per-asset configuration backups with revision history: NTLARS/DNC registry, part marker, UDC, CMM | Kind-pluggable per [BACKUP-KINDS.md](BACKUP-KINDS.md); a kind is one class in `services/registry.py`. Parseable kinds store a JSON projection and re-render to the native format on download; opaque vendor formats stay on the SFLD share with ShopDB holding metadata and the UNC pointer. Fed by the collector, so ingest authorizes on a `collector.ingest` service token, not a user JWT. `backups.view` and `backups.download` are separate permissions because a `.reg` is a restorable artifact. Not to be confused with [BACKUP-RESTORE.md](BACKUP-RESTORE.md), which is the ShopDB database itself. |
 
 ## Plugin permissions