Add logging service

New Go program (logger/) that:
- Accepts POSTed JSON log messages via POST /log
- Stores last N messages in a ring buffer (default 1M)
- Retrieves logs via GET /logs with limit/before/after filters
- Shows status via GET /status

Also updates express/logging.ts to POST messages to the logger service.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

logger/main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"strconv"
+)
+
+func main() {
+	port := flag.Int("port", 8085, "port to listen on")
+	capacity := flag.Int("capacity", 1000000, "max messages to store")
+
+	flag.Parse()
+
+	store := NewLogStore(*capacity)
+
+	http.HandleFunc("POST /log", func(w http.ResponseWriter, r *http.Request) {
+		var msg Message
+		if err := json.NewDecoder(r.Body).Decode(&msg); err != nil {
+			http.Error(w, "invalid JSON", http.StatusBadRequest)
+			return
+		}
+
+		store.Add(msg)
+		w.WriteHeader(http.StatusCreated)
+	})
+
+	http.HandleFunc("GET /logs", func(w http.ResponseWriter, r *http.Request) {
+		params := FilterParams{}
+
+		if limit := r.URL.Query().Get("limit"); limit != "" {
+			if n, err := strconv.Atoi(limit); err == nil {
+				params.Limit = n
+			}
+		}
+		if before := r.URL.Query().Get("before"); before != "" {
+			if ts, err := strconv.ParseInt(before, 10, 64); err == nil {
+				params.Before = ts
+			}
+		}
+		if after := r.URL.Query().Get("after"); after != "" {
+			if ts, err := strconv.ParseInt(after, 10, 64); err == nil {
+				params.After = ts
+			}
+		}
+
+		messages := store.GetFiltered(params)
+
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(messages)
+	})
+
+	http.HandleFunc("GET /status", func(w http.ResponseWriter, r *http.Request) {
+		status := map[string]any{
+			"count":    store.Count(),
+			"capacity": *capacity,
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(status)
+	})
+
+	listenAddr := fmt.Sprintf(":%d", *port)
+	log.Printf("[logger] Listening on %s (capacity: %d)", listenAddr, *capacity)
+	if err := http.ListenAndServe(listenAddr, nil); err != nil {
+		log.Fatalf("[logger] Failed to start: %v", err)
+	}
+}