Monorepo: consolidate 7 repos into one

Combines shared, blog, market, cart, events, federation, and account
into a single repository. Eliminates submodule sync, sibling model
copying at build time, and per-app CI orchestration.

Changes:
- Remove per-app .git, .gitmodules, .gitea, submodule shared/ dirs
- Remove stale sibling model copies from each app
- Update all 6 Dockerfiles for monorepo build context (root = .)
- Add build directives to docker-compose.yml
- Add single .gitea/workflows/ci.yml with change detection
- Add .dockerignore for monorepo build context
- Create __init__.py for federation and account (cross-app imports)

shared/alembic/versions/0009_add_slot_id_to_entries.py

@@ -0,0 +1,54 @@
+"""add slot_id to calendar_entries
+
+Revision ID: 0009_add_slot_id_to_entries
+Revises: 0008_add_flexible_to_slots
+Create Date: 2025-12-06 13:00:00.000000
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "0009_add_slot_id_to_entries"
+down_revision = "0008_add_flexible_to_slots"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Add slot_id column as nullable initially
+    op.add_column(
+        "calendar_entries",
+        sa.Column(
+            "slot_id",
+            sa.Integer(),
+            nullable=True,
+        ),
+    )
+    
+    # Add foreign key constraint
+    op.create_foreign_key(
+        "fk_calendar_entries_slot_id_calendar_slots",
+        "calendar_entries",
+        "calendar_slots",
+        ["slot_id"],
+        ["id"],
+        ondelete="SET NULL",
+    )
+    
+    # Add index for better query performance
+    op.create_index(
+        "ix_calendar_entries_slot_id",
+        "calendar_entries",
+        ["slot_id"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_calendar_entries_slot_id", table_name="calendar_entries")
+    op.drop_constraint(
+        "fk_calendar_entries_slot_id_calendar_slots",
+        "calendar_entries",
+        type_="foreignkey",
+    )
+    op.drop_column("calendar_entries", "slot_id")