Support base URL prefix via BASE_PATH

[GitBib]

Lingarr currently assumes it’s served from /. When deployed behind a reverse proxy under a subpath (e.g., /lingarr), absolute paths for static assets and the API break, redirects drop the prefix, and cookies are set without the correct Path.

Please add a single config parameter BASE_PATH (default /) that prefixes all application requests (API and static) and adjusts HTTP Location headers and cookie.Path accordingly. Acceptance: with any BASE_PATH, the app works entirely under /<BASE_PATH>/… without escaping to /; with BASE_PATH="/", behavior remains unchanged.

[rowanfuchs]

Thank you for the feature request. While it’s not requested often, I do see it as a potential option and will investigate.