feat: add configurable logging level for backend and Mini App

- Introduced a new `LOG_LEVEL` configuration option in the `.env.example` file to allow users to set the logging level (DEBUG, INFO, WARNING, ERROR).
- Updated the `Settings` class to include the `log_level` attribute, normalizing its value to ensure valid logging levels are used.
- Modified the logging setup in `run.py` to utilize the configured log level, enhancing flexibility in log management.
- Enhanced the Mini App to include the logging level in the JavaScript configuration, allowing for consistent logging behavior across the application.
- Added a new `logger.js` module for frontend logging, implementing level-based filtering and console delegation.
- Included unit tests for the new logger functionality to ensure proper behavior and level handling.

webapp/js/main.js

@@ -17,6 +17,7 @@ import {
 } from "./dom.js";
 import { showAccessDenied, hideAccessDenied, showError, setNavEnabled } from "./ui.js";
 import { fetchDuties, fetchCalendarEvents } from "./api.js";
+import { logger } from "./logger.js";
 import {
   dutiesByDate,
   calendarEventsByDate,
@@ -65,6 +66,8 @@ export function applyLangToUi() {
 
 applyLangToUi();
 
+logger.info("App init", "lang=" + state.lang);
+
 window.__dtReady = true;
 
 /**
@@ -148,6 +151,7 @@ async function loadMonth() {
   const from = localDateString(start);
   const to = localDateString(gridEnd);
   try {
+    logger.debug("Loading month", from, to);
     const dutiesPromise = fetchDuties(from, to, signal);
     const eventsPromise = fetchCalendarEvents(from, to, signal);
     const duties = await dutiesPromise;
@@ -186,6 +190,7 @@ async function loadMonth() {
       return;
     }
     if (e.message === "ACCESS_DENIED") {
+      logger.warn("Access denied in loadMonth", e.serverDetail);
       showAccessDenied(e.serverDetail);
       setNavEnabled(true);
       if (
@@ -198,6 +203,7 @@ async function loadMonth() {
       }
       return;
     }
+    logger.error("Load month failed", e);
     showError(e.message || t(state.lang, "error_generic"), loadMonth);
     setNavEnabled(true);
     return;