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>

migrations/versions/2025_01_21_0100-e5f6g7h8i9j0_add_hierarchical_locations.py

@@ -0,0 +1,61 @@
+"""Add hierarchical locations.
+
+Revision ID: e5f6g7h8i9j0
+Revises: d4e5f6g7h8i9
+Create Date: 2025-01-21 01:00:00.000000
+
+"""
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "e5f6g7h8i9j0"
+down_revision = "d4e5f6g7h8i9"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    """Create location table and add location_id to spool."""
+    # Create location table
+    op.create_table(
+        "location",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("name", sa.String(length=64), nullable=False),
+        sa.Column("parent_id", sa.Integer(), nullable=True),
+        sa.Column("location_type", sa.String(length=32), nullable=True),
+        sa.Column("description", sa.String(length=256), nullable=True),
+        sa.ForeignKeyConstraint(
+            ["parent_id"],
+            ["location.id"],
+            ondelete="SET NULL",
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_location_id"), "location", ["id"], unique=False)
+    op.create_index(op.f("ix_location_parent_id"), "location", ["parent_id"], unique=False)
+
+    # Add location_id column to spool table
+    op.add_column(
+        "spool",
+        sa.Column("location_id", sa.Integer(), nullable=True),
+    )
+    op.create_foreign_key(
+        "fk_spool_location_id",
+        "spool",
+        "location",
+        ["location_id"],
+        ["id"],
+        ondelete="SET NULL",
+    )
+    op.create_index(op.f("ix_spool_location_id"), "spool", ["location_id"], unique=False)
+
+
+def downgrade() -> None:
+    """Drop location table and remove location_id from spool."""
+    op.drop_index(op.f("ix_spool_location_id"), table_name="spool")
+    op.drop_constraint("fk_spool_location_id", "spool", type_="foreignkey")
+    op.drop_column("spool", "location_id")
+    op.drop_index(op.f("ix_location_parent_id"), table_name="location")
+    op.drop_index(op.f("ix_location_id"), table_name="location")
+    op.drop_table("location")