Add USB, Notifications, Network plugins and reusable EmployeeSearch component

New Plugins:
- USB plugin: Device checkout/checkin with employee lookup, checkout history
- Notifications plugin: Announcements with types, scheduling, shopfloor display
- Network plugin: Network device management with subnets and VLANs
- Equipment and Computers plugins: Asset type separation

Frontend:
- EmployeeSearch component: Reusable employee lookup with autocomplete
- USB views: List, detail, checkout/checkin modals
- Notifications views: List, form with recognition mode
- Network views: Device list, detail, form
- Calendar view with FullCalendar integration
- Shopfloor and TV dashboard views
- Reports index page
- Map editor for asset positioning
- Light/dark mode fixes for map tooltips

Backend:
- Employee search API with external lookup service
- Collector API for PowerShell data collection
- Reports API endpoints
- Slides API for TV dashboard
- Fixed AppVersion model (removed BaseModel inheritance)
- Added checkout_name column to usbcheckouts table

Styling:
- Unified detail page styles
- Improved pagination (page numbers instead of prev/next)
- Dark/light mode theme improvements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

shopdb/plugins/base.py

@@ -120,3 +120,31 @@ class BasePlugin(ABC):
         }
         """
         return []
+
+    def get_searchable_fields(self) -> List[Dict]:
+        """
+        Return fields this plugin contributes to global search.
+
+        Each field: {
+            'model': Type,           # SQLAlchemy model class
+            'field': str,            # Column name to search
+            'result_type': str,      # Type identifier for search results
+            'url_template': str,     # URL template with {id} placeholder
+            'title_field': str,      # Field to use for result title
+            'subtitle_field': str,   # Optional field for subtitle
+            'relevance_boost': int   # Optional relevance score multiplier
+        }
+
+        Example for equipment plugin:
+        return [{
+            'model': Equipment,
+            'join_model': Asset,
+            'join_condition': Equipment.assetid == Asset.assetid,
+            'search_fields': ['assetnumber', 'name', 'serialnumber'],
+            'result_type': 'equipment',
+            'url_template': '/equipment/{id}',
+            'title_field': 'assetnumber',
+            'subtitle_field': 'name',
+        }]
+        """
+        return []