Derive an asset's vendor from its catalog model, and show the model's own type

An asset that carries a model but no vendor was showing a blank the database
could already answer: the model records its vendor, and both sides reference the
same vendors table. Machines, PCs, printers and network devices now fall back to
it.

The fallback is FLAGGED, not merged silently. to_dict sets vendorfrommodel and
the detail pages render "(from model)" beside the value, because the record
itself is still empty: the edit form shows an empty vendor box, and a page
implying the vendor is stored would be lying about where it came from.

The model's type is exposed under its own name, modeltypename, and shown as a
separate "Model type" row. It is deliberately NOT used to fill in the asset's
own type. modeltypes is the catalog-wide list covering every kind of asset - it
holds "Access Point", "Camera" and "Desktop PC" alongside the machine entries -
so it is a different taxonomy from machinetypes. Only about two thirds of the
names overlap, and mapping one onto the other would mistype the remainder, with
the failure mode being a machine labelled "Desktop PC".

scripts/backfill_vendor_from_model.py writes the derived vendor down for real,
since the display fallback leaves reports that read vendorid still seeing
nothing. It is a dry run unless given --commit, fills only rows where the
asset's vendor is NULL and the model names one, and never overwrites a vendor
somebody chose. It skips a table lacking either column, so it runs against a
server whose network migration has not been applied yet.

Verified against the development database by nulling one machine's vendor inside
a transaction: it was detected as fillable, restored to exactly its original
value, and the rollback left the row untouched.

FLASK_ENV is not forced by the script. The app already reads it from .env, and
overriding it demanded a SECRET_KEY the environment had no reason to supply.

plugins/network/models/network_device.py

@@ -130,5 +130,17 @@ class NetworkDevice(BaseModel):
             result['modelname'] = self.model.modelnumber
             if self.model.imageurl:
                 result['imageurl'] = self.model.imageurl
+            # The catalog model already knows its maker, so an asset that has a
+            # model but no vendor of its own is showing a blank the database can
+            # fill. Flagged rather than merged silently: the edit form still has
+            # an empty vendor box, and a page implying otherwise would be lying.
+            if not self.vendor and self.model.vendor:
+                result['vendorname'] = self.model.vendor.vendor
+                result['vendorfrommodel'] = True
+            # Exposed under its OWN name. modeltypes is the catalog-wide list
+            # covering every kind of asset, so it is not interchangeable with
+            # this asset's own type and must never be substituted for it.
+            if self.model.modeltype:
+                result['modeltypename'] = self.model.modeltype.modeltype
 
         return result