show build on website footer

README.md

@@ -51,6 +51,7 @@ The app uses HTTP Basic Auth. Current credentials are defined in `BETA_USERS` in
 ├── app.py
 ├── requirements.txt
 ├── README.md
+├── build_info.json
 ├── access_log.json
 ├── config.json
 ├── article-data_.json
@@ -101,6 +102,7 @@ The template contains:
 
 - Page layout and all main CSS.
 - A disclaimer modal shown after Basic Auth login and before calculator use.
+- Footer build metadata from `build_info`.
 - Global state:
   - `window.ARTICLE_DATA`
   - `window.APP_CONFIG`
@@ -261,6 +263,19 @@ JSON audit log written by `app.py`.
 
 Important implementation detail: each logged access reads and rewrites the entire JSON file. This is simple but not concurrency-safe and can become inefficient as the file grows.
 
+### `build_info.json`
+
+Deployment/build metadata displayed in the site footer.
+
+Expected fields:
+
+- `version`
+- `branch`
+- `commit`
+- `timestamp`
+
+`app.py` loads this file centrally at startup and exposes it to all templates as `build_info`. If the file is missing, invalid, or a field is empty, the affected values fall back to `unknown` and the website continues to work.
+
 ### `fix_article_data.py`
 
 Utility script that updates relative frontend fetch/register paths to Flask-style `/static/...` paths and checks that key static files exist.