v0.22.1: dockerize defaults, harden error handling, fix test discovery

- config.py: defaults to localhost/localhost, AMQP to rabbitmq, secret
  path to /run/secrets, RAG_MAX_VECTORS from env
- rag.py: EMBED_URL default to localhost
- app.py: syslog handler wrapped in try/except
- routers/completions.py: db.close() in try/finally
- db.py: PRAGMA journal_mode = WAL
- amqp.py: subscription append before try for reconnect safety
- tests/conftest.py: add project root to sys.path for test discovery

db.py

@@ -29,6 +29,7 @@ def get_db():
     conn = sqlite3.connect(DB_PATH)
     conn.row_factory = sqlite3.Row
     conn.execute("PRAGMA foreign_keys = ON")
+    conn.execute("PRAGMA journal_mode = WAL")
     return conn