fix(web): pass plugin action params to the wrapper on stdin

POST /api/v3/plugins/action runs a plugin's script through a generated
Python wrapper, and the params went into that wrapper's source as
`params = <json.dumps(params)>`. JSON true, false and null are undefined
names in Python, so any params holding one made the wrapper die with a
NameError before the script ran, and the route answered "Action failed".
The plugin file manager's category toggle sends {"category_name": ...,
"enabled": true}, so of-the-day's category toggle failed every time.

The wrapper now reads the params from its own stdin (json.loads) and the
route passes them there; nothing taken from the request is written into
the generated source any more. The script's side is unchanged: the same
json.dumps(params) on its stdin, LEDMATRIX_ROOT set, stdout parsed.

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

CHANGELOG.md

@@ -549,6 +549,14 @@ policies are unchanged.
   screen showed first and the game came after it. Each check also asks each
   plugin `has_live_content()` once, where a plugin registered under several
   modes used to be asked once per mode.
+- A plugin action whose params hold `true`, `false` or `null` runs again.
+  `/api/v3/plugins/action` wrote the params into the source of the wrapper
+  that runs the plugin's script, and those JSON words are not Python, so the
+  wrapper stopped with a NameError and the action answered "Action failed".
+  The plugin file manager's category toggle sends `"enabled": true`, so
+  turning a category on or off in of-the-day always failed. The params now
+  reach the wrapper on its stdin; the script still receives them as JSON on
+  its own stdin, as before.
 - The display schedule turns the panel off at exactly the end time. A window
   now runs from its start time up to, but not including, its end time: with
   07:00-23:00 the panel is on at 07:00 and off at 23:00. Before, the end