feat: frontend LOG_LEVEL support via logger utility (#209)

- Inject LOG_LEVEL at build time via Vite define (__LOG_LEVEL__, default: warn)
- Create frontend logger utility (frontend/src/utils/logger.ts) mirroring backend API
- Replace all console.error calls with log.error in MedicationsPage, AppContext, Auth
- Supports levels: silent > error > warn > info > debug

Closes #205

frontend/src/components/Auth.tsx

@@ -1,5 +1,6 @@
 import { createContext, type ReactNode, useCallback, useContext, useEffect, useRef, useState } from "react";
 import { useTranslation } from "react-i18next";
+import { log } from "../utils/logger";
 import { ConfirmModal } from "./ConfirmModal";
 import { PasswordInput } from "./PasswordInput";
 
@@ -109,7 +110,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
 			}
 			setLoading(false);
 		} catch (err) {
-			console.error(`Failed to fetch auth state (attempt ${retryCount + 1}/${maxRetries + 1}):`, err);
+			log.error(`Failed to fetch auth state (attempt ${retryCount + 1}/${maxRetries + 1}):`, err);
 
 			// Retry on connection errors or 5xx errors (server might be restarting)
 			if (retryCount < maxRetries) {

frontend/src/context/AppContext.tsx

@@ -5,6 +5,7 @@ import { useAuth } from "../components/Auth";
 import { useCollapsedDays, useDoses, useMedications, useRefill, useSettings, useShare } from "../hooks";
 import type { Coverage, Medication, ScheduleEvent, StockThresholds } from "../types";
 import { getSystemLocale } from "../utils/formatters";
+import { log } from "../utils/logger";
 import { buildSchedulePreview, calculateCoverage, computeMissedPastDoseIds, isDoseDismissed } from "../utils/schedule";
 
 // =============================================================================
@@ -514,7 +515,7 @@ export function AppProvider({ children }: { children: React.ReactNode }) {
 				document.body.removeChild(a);
 				URL.revokeObjectURL(url);
 			} catch (err) {
-				console.error("Export error:", err);
+				log.error("Export error:", err);
 			}
 			setExporting(false);
 		},
@@ -568,7 +569,7 @@ export function AppProvider({ children }: { children: React.ReactNode }) {
 			try {
 				data = text ? JSON.parse(text) : {};
 			} catch {
-				console.error("Import response parse error:", text);
+				log.error("Import response parse error:", text);
 				alert(`${t("exportImport.importError")}: Server returned invalid response`);
 				return;
 			}
@@ -590,7 +591,7 @@ export function AppProvider({ children }: { children: React.ReactNode }) {
 			settingsHook.loadSettings();
 			doses.loadTakenDoses();
 		} catch (err) {
-			console.error("Import error:", err);
+			log.error("Import error:", err);
 			alert(t("exportImport.importError"));
 		}
 

frontend/src/pages/MedicationsPage.tsx

@@ -6,6 +6,7 @@ import { useMedicationForm, useUnsavedChangesWarning } from "../hooks";
 import type { DoseUnit, Medication } from "../types";
 import { DOSE_UNITS, FIELD_LIMITS, getPackageSize } from "../types";
 import { combineDateAndTime, formatDateTime, formatNumber } from "../utils/formatters";
+import { log } from "../utils/logger";
 
 export function MedicationsPage() {
 	const { t } = useTranslation();
@@ -299,7 +300,7 @@ export function MedicationsPage() {
 				setOriginalForm(form);
 			}
 		} catch (err) {
-			console.error("Save error:", err);
+			log.error("Save error:", err);
 			alert(err instanceof Error && err.message ? err.message : t("common.saveFailed"));
 		}
 

frontend/src/utils/logger.ts

@@ -0,0 +1,39 @@
+/**
+ * Frontend logger that respects LOG_LEVEL (injected at build time via Vite define).
+ * Mirrors the backend logger API so usage is consistent across the stack.
+ *
+ * Levels (high → low): silent > error > warn > info > debug
+ * Default: "warn" — only warn and error messages are shown.
+ */
+
+declare const __LOG_LEVEL__: string;
+
+const LOG_LEVELS: Record<string, number> = {
+	silent: 50,
+	error: 40,
+	warn: 30,
+	info: 20,
+	debug: 10,
+};
+
+const configuredLevel = typeof __LOG_LEVEL__ !== "undefined" ? __LOG_LEVEL__.toLowerCase() : "warn";
+const threshold = LOG_LEVELS[configuredLevel] ?? LOG_LEVELS.warn;
+
+function shouldLog(level: string): boolean {
+	return (LOG_LEVELS[level] ?? 0) >= threshold;
+}
+
+export const log = {
+	debug(...args: unknown[]): void {
+		if (shouldLog("debug")) console.debug(...args);
+	},
+	info(...args: unknown[]): void {
+		if (shouldLog("info")) console.info(...args);
+	},
+	warn(...args: unknown[]): void {
+		if (shouldLog("warn")) console.warn(...args);
+	},
+	error(...args: unknown[]): void {
+		if (shouldLog("error")) console.error(...args);
+	},
+};