feat: extract shared infrastructure from shared_lib

Phase 1-3 of decoupling plan:
- Shared DB, models, infrastructure, browser, config, utils
- Event infrastructure (domain_events outbox, bus, processor)
- Structured logging
- Generic container concept (container_type/container_id)
- Alembic migrations for all schema changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

alembic/versions/0005_add_description.py

@@ -0,0 +1,27 @@
+"""Add description field to orders"""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0005_add_description"
+down_revision = "0004_add_sumup_reference"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "orders",
+        sa.Column("description", sa.Text(), nullable=True),
+    )
+    op.create_index(
+        "ix_orders_description",
+        "orders",
+        ["description"],
+        unique=False,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_orders_description", table_name="orders")
+    op.drop_column("orders", "description")