Support exporting install configuration as environment variables for stateless deployments

## Is your feature request related to a problem? Please describe

Answer's installation flow generates `/data/conf/config.yaml`, and the Helm chart notes that persistence is required so `config.yaml` survives restarts. `AUTO_INSTALL` accepts environment variables for initial setup, but those variables are not used as the runtime configuration afterward.

This makes configuration-stateless container deployments difficult. A pod with a disposable filesystem cannot restart or scale from an already initialized external database using environment variables and secrets alone. Operators must persist or mount the generated `config.yaml`, or rerun the one-time installer, which is not appropriate once the database has already been initialized.

## Describe the solution you'd like

Please allow the install flow to export the effective post-install configuration as a complete, documented set of environment variables, and allow normal Answer startup to consume those variables without requiring `config.yaml`.

Expected behavior could include:

- An explicit install option or endpoint that exports the effective runtime configuration in a machine-readable environment-variable format, such as dotenv or shell output.
- An environment-variable equivalent for every `config.yaml` value required at runtime, with documented precedence when both sources are present.
- A fresh Answer instance can connect to an already initialized external database and start using only the exported environment variables, without a local `config.yaml`.
- Secrets are never printed to ordinary logs; exporting secret-bearing values requires an explicit action and can be directed to a secret manager.
- Existing `config.yaml`-based deployments remain backward compatible.

This would make Answer easier to run with immutable images, disposable pods, Kubernetes Secrets, and externally managed databases.

## Describe alternatives you've considered

- Persist `/data/conf` on a volume.
- Generate and mount `config.yaml` from a ConfigMap or Secret.
- Use an init container or entrypoint template to recreate `config.yaml` on every start.
- Keep using `AUTO_INSTALL`, although it is a one-time initialization path and fails or becomes inappropriate after the database has already been initialized.

The issue names no files or tests; start by tracing the installation flow, AUTO_INSTALL handling, config.yaml loading, and the Helm chart configuration. Done means runtime configuration can be exported and consumed through documented environment variables, supports an already initialized external database without config.yaml, preserves backward compatibility, and avoids exposing secrets in ordinary logs.

Written by the indexing model from the issue text.