feat: add inventory CSV import with warehouse/bin locations

- Add warehouse and bin_location columns to Inventory model
- Create inventory_import_service for bulk TSV/CSV import
- Add POST /api/v1/admin/inventory/import endpoint
- Add Import button and modal to inventory admin page
- Support both single-unit rows and explicit QUANTITY column

File format: BIN, EAN, PRODUCT (optional), QUANTITY (optional)
Products matched by GTIN/EAN, unmatched items reported.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

alembic/versions/e1bfb453fbe9_add_warehouse_and_bin_location_to_.py

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+"""add_warehouse_and_bin_location_to_inventory
+
+Revision ID: e1bfb453fbe9
+Revises: j8e9f0a1b2c3
+Create Date: 2025-12-25 12:21:24.006548
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy import text
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'e1bfb453fbe9'
+down_revision: Union[str, None] = 'j8e9f0a1b2c3'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+
+    # Check if columns already exist (idempotent)
+    result = conn.execute(text("PRAGMA table_info(inventory)"))
+    columns = {row[1] for row in result.fetchall()}
+
+    if 'warehouse' not in columns:
+        op.add_column('inventory', sa.Column('warehouse', sa.String(), nullable=False, server_default='strassen'))
+
+    if 'bin_location' not in columns:
+        op.add_column('inventory', sa.Column('bin_location', sa.String(), nullable=False, server_default=''))
+
+    # Migrate existing data: copy location to bin_location, set default warehouse
+    conn.execute(text("""
+        UPDATE inventory
+        SET bin_location = COALESCE(location, 'UNKNOWN'),
+            warehouse = 'strassen'
+        WHERE bin_location IS NULL OR bin_location = ''
+    """))
+
+    # Create indexes if they don't exist
+    indexes = conn.execute(text("PRAGMA index_list(inventory)"))
+    existing_indexes = {row[1] for row in indexes.fetchall()}
+
+    if 'idx_inventory_warehouse_bin' not in existing_indexes:
+        op.create_index('idx_inventory_warehouse_bin', 'inventory', ['warehouse', 'bin_location'], unique=False)
+    if 'ix_inventory_bin_location' not in existing_indexes:
+        op.create_index(op.f('ix_inventory_bin_location'), 'inventory', ['bin_location'], unique=False)
+    if 'ix_inventory_warehouse' not in existing_indexes:
+        op.create_index(op.f('ix_inventory_warehouse'), 'inventory', ['warehouse'], unique=False)
+
+
+def downgrade() -> None:
+    conn = op.get_bind()
+
+    # Check which indexes exist before dropping
+    indexes = conn.execute(text("PRAGMA index_list(inventory)"))
+    existing_indexes = {row[1] for row in indexes.fetchall()}
+
+    if 'ix_inventory_warehouse' in existing_indexes:
+        op.drop_index(op.f('ix_inventory_warehouse'), table_name='inventory')
+    if 'ix_inventory_bin_location' in existing_indexes:
+        op.drop_index(op.f('ix_inventory_bin_location'), table_name='inventory')
+    if 'idx_inventory_warehouse_bin' in existing_indexes:
+        op.drop_index('idx_inventory_warehouse_bin', table_name='inventory')
+
+    # Check if columns exist before dropping
+    result = conn.execute(text("PRAGMA table_info(inventory)"))
+    columns = {row[1] for row in result.fetchall()}
+
+    if 'bin_location' in columns:
+        op.drop_column('inventory', 'bin_location')
+    if 'warehouse' in columns:
+        op.drop_column('inventory', 'warehouse')