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/o5m3j9k1l2_add_origin_app_column.py

@@ -0,0 +1,35 @@
+"""Add origin_app column to ap_activities
+
+Revision ID: o5m3j9k1l2
+Revises: n4l2i8j0k1
+Create Date: 2026-02-22
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy import inspect as sa_inspect
+
+revision = "o5m3j9k1l2"
+down_revision = "n4l2i8j0k1"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+    inspector = sa_inspect(conn)
+    columns = [c["name"] for c in inspector.get_columns("ap_activities")]
+    if "origin_app" not in columns:
+        op.add_column(
+            "ap_activities",
+            sa.Column("origin_app", sa.String(64), nullable=True),
+        )
+    # Index is idempotent with if_not_exists
+    op.create_index(
+        "ix_ap_activity_origin_app", "ap_activities", ["origin_app"],
+        if_not_exists=True,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_ap_activity_origin_app", table_name="ap_activities")
+    op.drop_column("ap_activities", "origin_app")