Refactor local settings to dotenv-based gallery paths

AGENTS.md

@@ -28,19 +28,21 @@ This document is intentionally explicit so tasks can be completed with minimal r
 - Apply migrations: `python manage.py migrate`
 - Run server: `python manage.py runserver`
 
-Local configuration (`NibasaViewer/local_settings.py`) is required for real gallery usage:
+Local configuration is loaded from `.env` via `python-dotenv`.
 
-```python
-from pathlib import Path
+Use this minimum `.env` content for gallery paths:
 
-GALLERY_ROOT = Path('/path/to/images')
-THUMBNAILS_ROOT = Path('/path/to/thumb-cache')
-
-DEBUG = False
-ALLOWED_HOSTS = ['yourdomain.example']
-SECRET_KEY = 'replace-me'
+```env
+GALLERY_ROOT=/path/to/images
+THUMBNAILS_ROOT=/path/to/thumb-cache
 ```
 
+Notes:
+
+- `GALLERY_ROOT` and `THUMBNAILS_ROOT` are parsed as `pathlib.Path` in `settings.py`.
+- Both are optional at import time and default to `None` when unset/empty.
+- Paths do not need to be inside `BASE_DIR`.
+
 ## 4) Build / Lint / Test Commands
 
 There is no dedicated linter or formatter config in-repo (no `ruff`, `flake8`, `black`, `mypy`, `pyright`, `tox`, or `pytest` config files detected).
@@ -145,7 +147,7 @@ Notes:
 ## 9) Safety and Config Hygiene
 
 - Never commit secrets or production-specific local settings.
-- Keep `local_settings.py` local; defaults in `settings.py` should remain safe placeholders.
+- Keep `.env` local and out of version control; use `.env.example` as a template.
 - Avoid destructive git operations unless explicitly requested.
 - Do not revert unrelated working tree changes made by humans.