Initial implementation of inventree

A small IT asset inventory system built around a nested folder tree,
matching the project brief: Go + html/template + Bootstrap 5 + vanilla JS,
SQLite storage (WAL, FKs, migrations), embedded templates/static assets,
single compiled binary.

- AJAX-driven inventory tree: lazy-loaded folder expansion with per-user
  persisted expand state, drag-and-drop move for folders/assets, safe
  delete-with-relocate-or-cascade confirmation, search with breadcrumbs.
- Assets: CRUD, duplicate, move, auto-generated IT-000001-style IDs,
  CSV import (with optional folder auto-create) and export.
- Admin-defined item types with custom fields (text/long_text/number/date/
  boolean/dropdown/url/ip_address).
- Configurable statuses, session-based auth (bcrypt, secure cookies),
  admin/user roles, user management.
- CLI: serve, version, database migrate, database backup; /healthz;
  graceful shutdown; Dockerfile/docker-compose/systemd unit; Go test suite.

internal/web/helpers.go

@@ -0,0 +1,74 @@
+package web
+
+import (
+	"encoding/json"
+	"net/http"
+	"strconv"
+)
+
+func pathID(r *http.Request, name string) (int64, error) {
+	return strconv.ParseInt(r.PathValue(name), 10, 64)
+}
+
+// queryOptionalID parses a query parameter as *int64; an empty or missing
+// value returns nil (meaning "top level" / "unfiled" in folder/asset
+// contexts).
+func queryOptionalID(r *http.Request, name string) (*int64, error) {
+	v := r.URL.Query().Get(name)
+	if v == "" {
+		return nil, nil
+	}
+	id, err := strconv.ParseInt(v, 10, 64)
+	if err != nil {
+		return nil, err
+	}
+	return &id, nil
+}
+
+func queryInt64(r *http.Request, name string) int64 {
+	v := r.URL.Query().Get(name)
+	if v == "" {
+		return 0
+	}
+	id, _ := strconv.ParseInt(v, 10, 64)
+	return id
+}
+
+func queryInt(r *http.Request, name string, def int) int {
+	v := r.URL.Query().Get(name)
+	if v == "" {
+		return def
+	}
+	n, err := strconv.Atoi(v)
+	if err != nil {
+		return def
+	}
+	return n
+}
+
+type jsonEnvelope struct {
+	OK      bool   `json:"ok"`
+	Error   string `json:"error,omitempty"`
+	Message string `json:"message,omitempty"`
+	Data    any    `json:"data,omitempty"`
+}
+
+func writeJSON(w http.ResponseWriter, status int, v jsonEnvelope) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(v)
+}
+
+func jsonOK(w http.ResponseWriter, data any) {
+	writeJSON(w, http.StatusOK, jsonEnvelope{OK: true, Data: data})
+}
+
+func jsonErr(w http.ResponseWriter, status int, err error) {
+	writeJSON(w, status, jsonEnvelope{OK: false, Error: err.Error()})
+}
+
+func readJSON(r *http.Request, v any) error {
+	dec := json.NewDecoder(r.Body)
+	dec.DisallowUnknownFields()
+	return dec.Decode(v)
+}