feat(docker-watcher): phase 7 - deployer & health checker

Deploy orchestrator with full pipeline: pull → create container →
start → network → NPM proxy → health check. Rollback on failure,
multi-instance support, max_instances enforcement, webhook notifications.
Fix NPM auth in rollback and error logging in removeInstance.

internal/api/response.go

@@ -0,0 +1,47 @@
+package api
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+)
+
+// envelope is the standard API response wrapper.
+type envelope struct {
+	Success bool   `json:"success"`
+	Data    any    `json:"data,omitempty"`
+	Error   string `json:"error,omitempty"`
+}
+
+// respondJSON writes a JSON success response with the given status code and data.
+func respondJSON(w http.ResponseWriter, status int, data any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	if err := json.NewEncoder(w).Encode(envelope{Success: true, Data: data}); err != nil {
+		log.Printf("[api] encode response: %v", err)
+	}
+}
+
+// respondError writes a JSON error response with the given status code and message.
+func respondError(w http.ResponseWriter, status int, msg string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	if err := json.NewEncoder(w).Encode(envelope{Success: false, Error: msg}); err != nil {
+		log.Printf("[api] encode error response: %v", err)
+	}
+}
+
+// respondNotFound writes a 404 JSON error response for the given entity type.
+func respondNotFound(w http.ResponseWriter, entity string) {
+	respondError(w, http.StatusNotFound, entity+" not found")
+}
+
+// decodeJSON reads and decodes the request body into the given value.
+// Returns false and writes a 400 error response if decoding fails.
+func decodeJSON(w http.ResponseWriter, r *http.Request, v any) bool {
+	if err := json.NewDecoder(r.Body).Decode(v); err != nil {
+		respondError(w, http.StatusBadRequest, "invalid JSON: "+err.Error())
+		return false
+	}
+	return true
+}