feat: Listen on Unix Socket

[AWildLeon]

This pull request adds support for running the server on a Unix socket in addition to the existing TCP host:port option. The configuration, startup logic, and documentation have been updated to support this new mode while keeping validation strict to ensure only one listening method is used.

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Server listening mode enhancements

• Added support for listening on a Unix socket via the new socket-path configuration property in config.go, with validation to ensure that only one of socket-path or host:port is specified. [1] [2]
• Modified server startup logic in glance.go to handle Unix socket creation and cleanup, and to select between TCP and Unix socket based on configuration. [1] [2]

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Documentation updates

• Updated docs/configuration.md to document the new socket-path option.
• Added configuration examples for both TCP and Unix socket modes, and clarified that only one mode may be enabled at a time. [1] [2]

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Why Unix sockets?

The main motivation for this feature is to simplify reverse proxy setups. For example, a proxy (such as Caddy or Nginx) can be configured to talk directly to the server over a Unix domain socket instead of a TCP port. This avoids the need to open or manage additional firewall rules, which is especially convenient in NixOS environments or when running in containers.

More generally, Unix sockets provide:

• No TCP port required → reduced attack surface and simpler firewalling.
• Lower overhead for local communication (no IP stack traversal).
• File system–based access control via standard Unix permissions.
• A good fit for sandboxed/containerized deployments where networking may be restricted.

[AWildLeon]

Any Feedback welcome 😄