feat(server): handlers REST + transport MQTT

Ajout des handlers HTTP (agents, métriques historique, config agent/serveur, icônes upload/get) et du client MQTT serveur avec subscribe automatique et PushConfig.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/handlers/config.go

@@ -0,0 +1,83 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"strings"
+
+	"github.com/user/nanometrics/server/db"
+	"github.com/user/nanometrics/server/models"
+)
+
+func AgentConfigHandler(database *db.DB, pushConfig func(agentID string, cfg *models.AgentConfig)) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		parts := strings.Split(strings.Trim(r.URL.Path, "/"), "/")
+		if len(parts) < 4 {
+			http.Error(w, "invalid path", 400)
+			return
+		}
+		agentID := parts[2]
+
+		switch r.Method {
+		case http.MethodGet:
+			cfg, err := database.GetAgentConfig(agentID)
+			if err != nil {
+				http.Error(w, err.Error(), 500)
+				return
+			}
+			if cfg == nil {
+				cfg = &models.AgentConfig{}
+			}
+			w.Header().Set("Content-Type", "application/json")
+			json.NewEncoder(w).Encode(cfg)
+
+		case http.MethodPut:
+			var cfg models.AgentConfig
+			if err := json.NewDecoder(r.Body).Decode(&cfg); err != nil {
+				http.Error(w, err.Error(), 400)
+				return
+			}
+			if err := database.UpsertAgentConfig(agentID, &cfg); err != nil {
+				http.Error(w, err.Error(), 500)
+				return
+			}
+			if pushConfig != nil {
+				go pushConfig(agentID, &cfg)
+			}
+			w.WriteHeader(http.StatusNoContent)
+
+		default:
+			http.Error(w, "method not allowed", 405)
+		}
+	}
+}
+
+func ServerConfigHandler(database *db.DB) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		switch r.Method {
+		case http.MethodGet:
+			cfg, err := database.GetServerConfig()
+			if err != nil {
+				http.Error(w, err.Error(), 500)
+				return
+			}
+			w.Header().Set("Content-Type", "application/json")
+			json.NewEncoder(w).Encode(cfg)
+
+		case http.MethodPut:
+			var cfg models.ServerConfig
+			if err := json.NewDecoder(r.Body).Decode(&cfg); err != nil {
+				http.Error(w, err.Error(), 400)
+				return
+			}
+			if err := database.SetServerConfig(cfg); err != nil {
+				http.Error(w, err.Error(), 500)
+				return
+			}
+			w.WriteHeader(http.StatusNoContent)
+
+		default:
+			http.Error(w, "method not allowed", 405)
+		}
+	}
+}