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/0008_add_flexible_to_slots.py

@@ -0,0 +1,33 @@
+"""add flexible flag to calendar_slots
+
+Revision ID: 0008_add_flexible_to_calendar_slots
+Revises: 0007_add_order_id_to_calendar_entries
+Create Date: 2025-12-06 12:34:56.000000
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "0008_add_flexible_to_slots"
+down_revision = "0007_add_oid_entries"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "calendar_slots",
+        sa.Column(
+            "flexible",
+            sa.Boolean(),
+            nullable=False,
+            server_default=sa.false(),  # set existing rows to False
+        ),
+    )
+    # Optional: drop server_default so future inserts must supply a value
+    op.alter_column("calendar_slots", "flexible", server_default=None)
+
+
+def downgrade() -> None:
+    op.drop_column("calendar_slots", "flexible")