Add collector PC->printer links and searchable custom fields

Collector: the computers collector schema gains defaultprinter and
printers; apply_collector_payload resolves each reported identifier to
a printer asset (windowsname/hostname/sharename/assetnumber/IP,
first-hit case-insensitive) and idempotently syncs relationships -
defaultprinter (directional) for the default, connectedto for the
rest. Collector-created rows are tagged so a re-report archives dropped
links while manual relationships are never touched; unresolved
identifiers warn instead of failing. Both PC and printer detail pages
show the links via the shared relationships card (no frontend change).
GE-Enforce Win32_Printer collection snippet documented.

Searchable custom fields: a per-field searchable flag (migration 7d24);
global search matches custom-field values on flagged active fields and
routes each hit to the asset detail page, reusing the existing
(type,id) dedupe and search_<type>_enabled domain filter. Searchable
toggle on the Custom Fields settings page.

822 tests pass; both verified live.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

shopdb/core/api/customfields.py

@@ -87,6 +87,7 @@ def create_field():
             existing.options = _normalize_options(data.get('options'))
             existing.showondetail = bool(data.get('showondetail', True))
             existing.showonform = bool(data.get('showonform', True))
+            existing.searchable = bool(data.get('searchable', False))
             existing.sortorder = data.get('sortorder', 0)
             db.session.commit()
             return success_response(existing.to_dict(), message='Reactivated existing field')
@@ -101,6 +102,7 @@ def create_field():
         options=_normalize_options(data.get('options')),
         showondetail=bool(data.get('showondetail', True)),
         showonform=bool(data.get('showonform', True)),
+        searchable=bool(data.get('searchable', False)),
         sortorder=data.get('sortorder', 0),
     )
     db.session.add(field)
@@ -124,7 +126,7 @@ def update_field(fieldid):
         field.datatype = data['datatype']
     if 'options' in data:
         field.options = _normalize_options(data['options'])
-    for key in ('showondetail', 'showonform', 'isactive'):
+    for key in ('showondetail', 'showonform', 'isactive', 'searchable'):
         if key in data:
             setattr(field, key, bool(data[key]))
     if 'sortorder' in data: