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/0001_initial_schem.py

@@ -0,0 +1,33 @@
+"""Initial database schema from schema.sql"""
+
+from alembic import op
+import sqlalchemy as sa
+import pathlib
+
+# revision identifiers, used by Alembic
+revision = '0001_initial_schema'
+down_revision = None
+branch_labels = None
+depends_on = None
+
+def upgrade():
+    return
+    schema_path = pathlib.Path(__file__).parent.parent.parent / "schema.sql"
+    with open(schema_path, encoding="utf-8") as f:
+        sql = f.read()
+    conn = op.get_bind()
+    conn.execute(sa.text(sql))
+
+def downgrade():
+    return
+    # Drop all user-defined tables in the 'public' schema
+    conn = op.get_bind()
+    conn.execute(sa.text("""
+        DO $$ DECLARE
+            r RECORD;
+        BEGIN
+            FOR r IN (SELECT tablename FROM pg_tables WHERE schemaname = 'public') LOOP
+                EXECUTE 'DROP TABLE IF EXISTS public.' || quote_ident(r.tablename) || ' CASCADE';
+            END LOOP;
+        END $$;
+    """))