Statuses import, an icon picker, folder-scoped CSV import, and site name

- Statuses can now be bulk-imported/updated via CSV (Name, Color columns;
  matches and updates existing statuses by name). New
  internal/statuses/csv.go, tested.
- Icon fields (folder create/rename, item type form) are now a searchable
  dropdown of the 50 most common Bootstrap Icons instead of a free-text
  box, via a small reusable .icon-picker widget in app.js/app.css.
- CSV asset import is now folder-scoped when triggered from the tree:
  right-click a folder (or its background) > Import CSV... imports every
  row directly into that folder, so the CSV needs no Folder column at
  all, and the option no longer appears at the top level. The original
  global, Folder-path-aware import (with auto-create-missing-folders)
  moved to a new admin-only Settings > Import / Export page, alongside
  the new Statuses import and format examples for both. assets.Import
  gained ImportOptions.TargetFolderID to drive the folder-scoped mode.
- Site Name (Settings > General) now actually renders in the navbar
  brand and <title>, via a per-App "siteName" template func bound in
  loadTemplates. The brand is plain text now, not a link to /inventory.

internal/web/helpers.go

@@ -25,6 +25,20 @@ func queryOptionalID(r *http.Request, name string) (*int64, error) {
 	return &id, nil
 }
 
+// formOptionalID parses a POST form/multipart-form field (already parsed via
+// ParseForm/ParseMultipartForm) as *int64; empty or missing returns nil.
+func formOptionalID(r *http.Request, name string) (*int64, error) {
+	v := r.FormValue(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 == "" {