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)

federation/Dockerfile

@@ -0,0 +1,50 @@
+# syntax=docker/dockerfile:1
+
+# ---------- Python application ----------
+FROM python:3.11-slim AS base
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1 \
+    PYTHONPATH=/app \
+    PIP_NO_CACHE_DIR=1 \
+    APP_PORT=8000 \
+    APP_MODULE=app:app
+
+WORKDIR /app
+
+# Install system deps + psql client
+RUN apt-get update && apt-get install -y --no-install-recommends \
+      ca-certificates \
+      postgresql-client \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY shared/requirements.txt ./requirements.txt
+RUN pip install -r requirements.txt
+
+# Shared code (replaces submodule)
+COPY shared/ ./shared/
+
+# App code
+COPY federation/ ./
+
+# Sibling models for cross-domain SQLAlchemy imports
+COPY blog/__init__.py ./blog/__init__.py
+COPY blog/models/ ./blog/models/
+COPY market/__init__.py ./market/__init__.py
+COPY market/models/ ./market/models/
+COPY cart/__init__.py ./cart/__init__.py
+COPY cart/models/ ./cart/models/
+COPY events/__init__.py ./events/__init__.py
+COPY events/models/ ./events/models/
+COPY account/__init__.py ./account/__init__.py
+COPY account/models/ ./account/models/
+
+# ---------- Runtime setup ----------
+COPY federation/entrypoint.sh /usr/local/bin/entrypoint.sh
+RUN chmod +x /usr/local/bin/entrypoint.sh
+
+RUN useradd -m -u 10001 appuser && chown -R appuser:appuser /app
+USER appuser
+
+EXPOSE ${APP_PORT}
+ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]