feat(parts): couple state and location (host vs bin)

DEPLOYED parts live on a host; every other state lives in a bin (or
unassigned). Previously binId and hostId were independent nullable
fields with no validation, so the Edit Part dialog could leave a
DEPLOYED part with only a bin and no host — which silently dropped
it from the repair problem-part picker.

- Service: resolveLocation() helper enforces the invariant on create
  and update. On a state transition, update auto-clears the stale
  relation and emits LOCATION_CHANGED for the cleared side.
- Zod: CreatePartRequest.superRefine rejects mismatched state/location
  up front; UpdatePartRequest rejects both-fields-set.
- Web: PartFormDialog swaps a single Location field between Host
  combobox (DEPLOYED) and Bin combobox (others); switching State
  clears the opposite field. Parts list + detail render host first,
  then bin path, then Unassigned.
- Tests: 9 new cases covering the invariant including the no-op guard
  so an unrelated PATCH on a DEPLOYED part doesn't touch hostId/binId.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/src/pages/Parts.tsx

@@ -116,6 +116,14 @@ export default function Parts() {
         id: 'location',
         header: 'Location',
         cell: ({ row }) => {
+          const host = row.original.host;
+          if (host) {
+            return (
+              <span className="text-xs font-mono text-muted-foreground">
+                {host.assetId} / {host.name}
+              </span>
+            );
+          }
           const path = row.original.bin?.fullPath;
           return path ? (
             <span className="text-xs font-mono text-muted-foreground">{path}</span>