fix(print-modal): map each plate on its own, and show the panel that does it (#2551)

Selecting several plates hid the filament mapping panel but did not stop the
modal sending a mapping. With no single plate selected it fell back to the
whole file's filament list -- the union of every plate -- and matched against
that. Tray assignment is stateful, so where plate 1 prints red on slot 1 and
plate 2 prints red on slot 2, slot 1 claimed the only red spool and slot 2 fell
through to a type-only match on black. That one mapping went out with every
plate, and the scheduler uses a stored mapping verbatim, so plate 2 printed in
the wrong colour -- decided by a panel the user never saw.

Fetch each selected plate's requirements and map them separately: one panel per
plate, named after it, with its own tray overrides, and each queue item carries
its own plate's mapping. A fan-out across several printers would be a panel per
plate per printer, so those items carry no mapping and the scheduler maps each
plate against the printer it picks. Model mode is unchanged -- no printer means
no trays to map onto.

The tray matcher existed twice and this needed a third caller, so extract it
once and have both existing paths delegate; its 62 tests pass unchanged.

The bug only reproduces with a realistic query cache -- the shared test harness
sets gcTime: 0, which evicts the union and makes the modal look innocent -- so
the new modal tests bring their own client.

static/index.html

@@ -26,7 +26,7 @@
 
     <!-- Splash screens for iOS -->
     <link rel="apple-touch-startup-image" href="/img/android-chrome-512x512.png" />
-    <script type="module" crossorigin src="/assets/index-xvC2pmGi.js"></script>
+    <script type="module" crossorigin src="/assets/index-CCULKpLm.js"></script>
     <link rel="stylesheet" crossorigin href="/assets/index-DASc8Ke0.css">
   </head>
   <body>