Initial scaffold with per-nameserver DNS monitoring model

Full project structure following upaas conventions: uber/fx DI, go-chi
routing, slog logging, Viper config. State persisted as JSON file with
per-nameserver record tracking for inconsistency detection. Stub
implementations for resolver, portcheck, tlscheck, and watcher.

internal/handlers/handlers.go

@@ -0,0 +1,58 @@
+// Package handlers provides HTTP request handlers.
+package handlers
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+
+	"go.uber.org/fx"
+
+	"sneak.berlin/go/dnswatcher/internal/globals"
+	"sneak.berlin/go/dnswatcher/internal/healthcheck"
+	"sneak.berlin/go/dnswatcher/internal/logger"
+)
+
+// Params contains dependencies for Handlers.
+type Params struct {
+	fx.In
+
+	Logger      *logger.Logger
+	Globals     *globals.Globals
+	Healthcheck *healthcheck.Healthcheck
+}
+
+// Handlers provides HTTP request handlers.
+type Handlers struct {
+	log     *slog.Logger
+	params  *Params
+	globals *globals.Globals
+	hc      *healthcheck.Healthcheck
+}
+
+// New creates a new Handlers instance.
+func New(_ fx.Lifecycle, params Params) (*Handlers, error) {
+	return &Handlers{
+		log:     params.Logger.Get(),
+		params:  &params,
+		globals: params.Globals,
+		hc:      params.Healthcheck,
+	}, nil
+}
+
+func (h *Handlers) respondJSON(
+	writer http.ResponseWriter,
+	_ *http.Request,
+	data any,
+	status int,
+) {
+	writer.Header().Set("Content-Type", "application/json")
+	writer.WriteHeader(status)
+
+	if data != nil {
+		err := json.NewEncoder(writer).Encode(data)
+		if err != nil {
+			h.log.Error("json encode error", "error", err)
+		}
+	}
+}

internal/handlers/healthcheck.go

@@ -0,0 +1,17 @@
+package handlers
+
+import (
+	"net/http"
+)
+
+// HandleHealthCheck returns the health check handler.
+func (h *Handlers) HandleHealthCheck() http.HandlerFunc {
+	return func(
+		writer http.ResponseWriter,
+		request *http.Request,
+	) {
+		h.respondJSON(
+			writer, request, h.hc.Check(), http.StatusOK,
+		)
+	}
+}

internal/handlers/status.go

@@ -0,0 +1,23 @@
+package handlers
+
+import (
+	"net/http"
+)
+
+// HandleStatus returns the monitoring status handler.
+func (h *Handlers) HandleStatus() http.HandlerFunc {
+	type response struct {
+		Status string `json:"status"`
+	}
+
+	return func(
+		writer http.ResponseWriter,
+		request *http.Request,
+	) {
+		h.respondJSON(
+			writer, request,
+			&response{Status: "ok"},
+			http.StatusOK,
+		)
+	}
+}