feat: add structured backend logging

Collector failures, service-API errors, WS connection lifecycle, and
config reload/discovery events were previously invisible outside the
browser (or, for a few config/discovery cases, logged with an
inconsistent ad-hoc console.error). Add a small scoped logger
(lib/logger.ts, level via LOG_LEVEL) and wire it through server.ts,
the scheduler, service collector, config loader/effective store, and
the WS server so operators can see failures via `docker logs`.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/collectors/scheduler.ts

@@ -7,6 +7,9 @@ import { collectSystem } from "./system";
 import { collectHttp } from "./http";
 import { collectService } from "./service";
 import type { WidgetResult } from "@/lib/types/widget-result";
+import { createLogger } from "@/lib/logger";
+
+const log = createLogger("scheduler");
 
 const httpLimit = pLimit(8);
 
@@ -122,6 +125,12 @@ class CollectorScheduler {
 
       if (existing) clearInterval(existing.timer);
 
+      log.debug(existing ? "job replaced" : "job added", {
+        widgetId: instance.id,
+        type: instance.widget.type,
+        intervalMs,
+      });
+
       const run = () => this.runJob(instance.id);
       const timer = setInterval(run, intervalMs);
       this.jobs.set(instance.id, { widget: instance.widget, intervalMs, timer, consecutiveFailures: 0 });
@@ -130,16 +139,20 @@ class CollectorScheduler {
 
     for (const [id, job] of this.jobs) {
       if (!seen.has(id)) {
+        log.debug("job removed", { widgetId: id, type: job.widget.type });
         clearInterval(job.timer);
         this.jobs.delete(id);
         this.lastResults.delete(id);
       }
     }
+
+    log.info("reconciled", { jobs: this.jobs.size });
   }
 
   stop(): void {
     for (const job of this.jobs.values()) clearInterval(job.timer);
     this.jobs.clear();
+    log.info("scheduler stopped");
   }
 
   private async runJob(id: string): Promise<void> {
@@ -150,10 +163,37 @@ class CollectorScheduler {
     try {
       result = await collect(job.widget);
       if (result.type === "http") {
+        const wasFailing = job.consecutiveFailures > 0;
         job.consecutiveFailures = result.data.up ? 0 : job.consecutiveFailures + 1;
         result = { type: "http", data: { ...result.data, consecutiveFailures: job.consecutiveFailures } };
+        if (!result.data.up) {
+          log.warn("http check failed", {
+            widgetId: id,
+            url: (job.widget as { url?: string }).url,
+            statusCode: result.data.statusCode,
+            attempt: job.consecutiveFailures,
+          });
+        } else if (wasFailing) {
+          log.info("http check recovered", { widgetId: id, url: (job.widget as { url?: string }).url });
+        }
+      } else {
+        if (job.consecutiveFailures > 0) {
+          log.info("collector recovered", {
+            widgetId: id,
+            type: job.widget.type,
+            afterFailures: job.consecutiveFailures,
+          });
+        }
+        job.consecutiveFailures = 0;
       }
     } catch (err) {
+      job.consecutiveFailures += 1;
+      log.error("collector failed", {
+        widgetId: id,
+        type: job.widget.type,
+        attempt: job.consecutiveFailures,
+        error: (err as Error).message,
+      });
       result = { type: "error", message: (err as Error).message };
     }