Let the warranty search find a machine number

Reported: the warranty page cannot be searched by machine number.

It was there to be found. _related_machine puts the machine's number in the
payload, and it does so for a stated reason - a shopfloor PC is bought,
warranted and replaced as a PC, but it is FOUND by the machine it drives, and
nobody walks the floor looking for an asset number. The table renders it as a
chip. The filter looked at vendor, service level, service tag and asset number,
and never at the machine. So the one identifier the feature was designed around
was the one thing the search box could not match.

This is how a field list goes wrong: a column was added to the table and not to
the filter, and nothing connects the two. Moved the field list into
warrantySearch.js so a test can see it, following controllingPc.js and
labelPages.js. Machine name is searched as well - somebody who knows the bay by
"the Makino" should not have to look up its number to find its warranty.

The specs also pin the case that made the old inline version fragile: a covered
asset whose machine is null, which is every printer and any PC nobody has linked
yet, must not throw. And a missing field must not match: String(undefined) is
'undefined', so a naive coercion makes a search for "und" hit every row with an
empty vendor.

Not changed, worth knowing: the covered asset's NAME is still not searched, only
its number. That looks like the same omission, but it is a wider change than the
report - the placeholder has always said "asset" without saying which half - so
it is left for a deliberate decision rather than folded in here.

CHANGELOG.md

@@ -105,6 +105,13 @@ ADR-007 and ADR-002.
   the wrong code. The page index now travels with the page.
 - The back label's dotted preview outline outspecified the print reset and drew
   a dashed rule down the edge of every second card.
+- **The warranty list could not be searched by machine number.** The number was
+  in the payload and rendered in the table as a chip, but the search box looked
+  only at vendor, service level, service tag and asset number. That made the
+  identifier the feature was built around - a shopfloor PC is warranted as a PC
+  but found by the machine it drives - the one thing the box could not find.
+  Machine number and machine name are now searched too, and the placeholder
+  names them.
 - **`flask plugin upgrade-all` failed a plugin whose tables already existed**
   ("table securesendsecrets already exists" on the tools plugin). Every
   post-cutover baseline emitted a plain `op.create_table`, which is correct only