[license] client/simple: SPDX-License-Identifier: AGPL-3.0-or-later

SPDX short-form identifiers to communicate license information in a simple,
efficient, portable and machine-readable manner [1]

[1] https://spdx.dev/learn/handling-license-info/

client/simple/tools/jinja_svg_catalog.html.edge

@@ -1,4 +1,6 @@
 {{--
+SPDX-License-Identifier: AGPL-3.0-or-later
+
 This is a EDGE https://edgejs.dev/ template to generate a HTML Jinja template
 for the backend.  Example output of this EDGE template:
 - https://github.com/searxng/searxng/blob/master/searx/templates/simple/icons.html