Add configurable structured logging

Adds a leveled JSON logger (error/warn/info/verbose/debug, controlled via
LOG_LEVEL) wired into the Express API (access log, error middleware,
crash handlers, memory heartbeat) and the Next.js server (page-request
proxy, instrumentation crash handlers, heartbeat). LOG_LEVEL is exposed
through compose.yaml, and both services now rotate their Docker logs
(json-file, 20m x 10 files) instead of growing unbounded. Intended to
capture long-running diagnostic data for the intermittent 502s seen on
the Docker host.

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

tests/logger.test.ts

@@ -0,0 +1,83 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import { createLogger, resolveLogLevel } from "../src/shared/logging/logger.js";
+
+describe("resolveLogLevel", () => {
+  it("defaults to info for missing or unknown values", () => {
+    assert.equal(resolveLogLevel(undefined), "info");
+    assert.equal(resolveLogLevel(""), "info");
+    assert.equal(resolveLogLevel("nonsense"), "info");
+  });
+
+  it("accepts known levels case-insensitively", () => {
+    assert.equal(resolveLogLevel("DEBUG"), "debug");
+    assert.equal(resolveLogLevel(" verbose "), "verbose");
+    assert.equal(resolveLogLevel("warn"), "warn");
+  });
+});
+
+describe("createLogger", () => {
+  it("suppresses levels below the configured threshold", () => {
+    const infoLines: string[] = [];
+    const originalLog = console.log;
+    console.log = (line: string) => {
+      infoLines.push(line);
+    };
+    try {
+      const logger = createLogger("test", { level: "warn" });
+      logger.info("should not appear");
+      logger.debug("should not appear");
+      logger.verbose("should not appear");
+    } finally {
+      console.log = originalLog;
+    }
+    assert.equal(infoLines.length, 0);
+  });
+
+  it("emits enabled levels as structured JSON with scope and meta", () => {
+    const errorLines: string[] = [];
+    const originalError = console.error;
+    console.error = (line: string) => {
+      errorLines.push(line);
+    };
+    try {
+      const logger = createLogger("test", { level: "warn" });
+      logger.warn("something happened", { code: 42 });
+    } finally {
+      console.error = originalError;
+    }
+    assert.equal(errorLines.length, 1);
+    const parsed = JSON.parse(errorLines[0]);
+    assert.equal(parsed.level, "warn");
+    assert.equal(parsed.scope, "test");
+    assert.equal(parsed.message, "something happened");
+    assert.equal(parsed.code, 42);
+    assert.equal(typeof parsed.timestamp, "string");
+  });
+
+  it("routes debug/verbose/info to console.log and error/warn to console.error", () => {
+    const logLines: string[] = [];
+    const errorLines: string[] = [];
+    const originalLog = console.log;
+    const originalError = console.error;
+    console.log = (line: string) => {
+      logLines.push(line);
+    };
+    console.error = (line: string) => {
+      errorLines.push(line);
+    };
+    try {
+      const logger = createLogger("test", { level: "debug" });
+      logger.debug("d");
+      logger.verbose("v");
+      logger.info("i");
+      logger.warn("w");
+      logger.error("e");
+    } finally {
+      console.log = originalLog;
+      console.error = originalError;
+    }
+    assert.equal(logLines.length, 3);
+    assert.equal(errorLines.length, 2);
+  });
+});