[no bump] Move technical docs to docs/, add icon and PNG export tool

README now carries the icon, TL;DR, description and features; the
technical sections live in docs/. tools/icon_png.py renders
images/icon.svg to a square PNG (512x512 by default, --resolution N).
plugin.json points at the plugin's own icon.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugin.json

@@ -2,9 +2,9 @@
   "id": "unlocked_restrictions",
   "name": "Unlocked Restrictions",
   "description": "Allows screenshots and forwarding (as a copy) in chats with protected content",
-  "author": "lyuksovannyy",
+  "author": "@lyuksovannyy",
   "version": "1.0.0",
-  "icon": "exteraPlugins/1",
+  "icon": "exteraGramPluginIcons/2",
   "app_version": ">=12.5.1",
   "sdk_version": ">=1.4.4.3",
   "requirements": []