fix(api): add snake_case json tags to Endpoint/Task/request bodies for frontend contract

Go's encoding/json does not bridge snake_case <-> PascalCase field names,
so store.Endpoint, store.Task and the anonymous request bodies in
accounts.go/auth.go were silently decoding empty/zero values from the
frontend's snake_case JSON contract (tls_mode, role_label,
src_endpoint_id, dst_endpoint_id, src_login/pass, dst_login/pass).
Adds explicit json tags; DB layer is unaffected since pgx binds by
positional params, not struct-tag reflection.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMHQTtnQtQqL8muAXHr9kd

internal/httpapi/accounts.go

@@ -40,7 +40,10 @@ func (s *Server) handleCreateAccount(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	var body struct {
-		SrcLogin, SrcPass, DstLogin, DstPass string
+		SrcLogin string `json:"src_login"`
+		SrcPass  string `json:"src_pass"`
+		DstLogin string `json:"dst_login"`
+		DstPass  string `json:"dst_pass"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		http.Error(w, "bad json", http.StatusBadRequest)

internal/httpapi/auth.go

@@ -27,7 +27,10 @@ func NewServer(cfg config.Config, s *store.Store, orch *orchestrator.Orchestrato
 }
 
 func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
-	var body struct{ User, Pass string }
+	var body struct {
+		User string `json:"user"`
+		Pass string `json:"pass"`
+	}
 	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 		http.Error(w, "bad json", http.StatusBadRequest)
 		return