fix(#12): Implement structured logging with request correlation and security event marking

docs/adr/structured-logging.md

@@ -0,0 +1,22 @@
+# Structured Logging
+
+## Status
+
+Accepted
+
+## Context
+
+For operational debugging, structured logs are needed for API errors and security events. This includes timestamps, log levels, request IDs, and routes.
+
+## Decision
+
+We implement a centralized logging middleware that:
+1. Logs all requests with timestamp, method, URL, request ID, and route
+2. Logs error responses with correlation via request ID
+3. Marks security-relevant events (401, 403) separately
+
+## Consequences
+
+- Logs are structured and filterable
+- Security events can be easily identified
+- Debugging is improved through correlation of requests and errors