Restructure chat service, web routes, and add test suite

Split monolithic chat service into modular structure with Matrix client
support, extract web server into per-resource route modules, introduce
bootstrap/main-loop separation, and add comprehensive vitest coverage
across services, repositories, and utilities. Adds project docs and
CLAUDE.md agent instructions.

src/utils/logger.ts

@@ -2,6 +2,22 @@ import winston from 'winston';
 
 export type Logger = winston.Logger;
 
+function safeStringify(value: unknown): string {
+  const seen = new WeakSet<object>();
+  try {
+    return JSON.stringify(value, (_key, val) => {
+      if (typeof val === 'object' && val !== null) {
+        if (seen.has(val)) return '[Circular]';
+        seen.add(val);
+      }
+      if (typeof val === 'bigint') return val.toString();
+      return val;
+    });
+  } catch (err) {
+    return `[Unserializable: ${(err as Error).message}]`;
+  }
+}
+
 export function createLogger(): Logger {
   return winston.createLogger({
     level: process.env.LOG_LEVEL || 'info',
@@ -15,7 +31,7 @@ export function createLogger(): Logger {
         format: winston.format.combine(
           winston.format.colorize(),
           winston.format.printf(({ level, message, timestamp, ...meta }) => {
-            const metaStr = Object.keys(meta).length ? ` ${JSON.stringify(meta)}` : '';
+            const metaStr = Object.keys(meta).length ? ` ${safeStringify(meta)}` : '';
             return `${timestamp} [${level}]: ${message}${metaStr}`;
           })
         ),