feat: single container image (nginx + backend), fix fresh DB init

- deploy/Dockerfile: unified image with supervisord (nginx + uvicorn)
- distribution/docker-compose.single.yml: single container option
- distribution/README.md: 3 deployment options (single, compose, docker run)
- Fix: add status column to chat_messages CREATE TABLE (was only in migration, broke fresh DB)
- push-images.sh: builds 3 images (unified, backend, frontend)

backend/app.py

@@ -310,6 +310,7 @@ def init_db():
             user_id TEXT NOT NULL, role TEXT NOT NULL,
             content TEXT NOT NULL,
             model_id TEXT,
+            status TEXT DEFAULT 'done',
             created_at TEXT DEFAULT (datetime('now'))
         );
         CREATE TABLE IF NOT EXISTS chat_summaries (