feat: Add batch operations, dashboard redesign, hierarchical locations

## Batch Operations (#13)
- Add POST /spool/bulk/archive, /bulk/delete, /bulk/update endpoints
- Add row selection with checkboxes to spool list
- Add floating BatchActionBar with archive/unarchive/delete/move actions
- Add confirmation modals for all batch operations

## Dashboard Redesign (#12)
- Install recharts for pie charts
- Add AlertCards (low stock, pending jobs, needs weighing)
- Add MaterialDistributionChart (pie chart by material)
- Add QuickStats row (total spools, filaments, vendors, weight)
- Refactor home page layout with new components

## Hierarchical Locations (#9)
- Add Location model with self-referential parent relationship
- Add migration for location table and spool.location_id FK
- Add location database operations (CRUD, tree, full path)
- Add location API endpoints (list, tree, CRUD)
- Add LocationTreeSelect component with nested tree display
- Add LocationCreateModal for inline location creation
- Keep legacy location string field for backward compatibility

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

client/package.json

@@ -33,6 +33,7 @@
     "react-i18next": "^16.5.1",
     "react-router": "^7.11.0",
     "react-to-print": "^3.2.0",
+    "recharts": "^3.7.0",
     "uuid": "^13.0.0",
     "vite-plugin-svgr": "^4.5.0",
     "zustand": "^5.0.9"