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>

web_interface/blueprints/api_v3/plugins.py

@@ -430,6 +430,10 @@ sys.exit(proc.returncode)
                     import tempfile
                     import json as json_lib
 
+                    # The params reach the wrapper on its stdin, never in
+                    # its source: written there as `params = <JSON>`, a
+                    # true, false or null was an undefined name and the
+                    # wrapper died with a NameError before the script ran.
                     params_json = json_lib.dumps(action_params)
                     with tempfile.NamedTemporaryFile(mode='w', suffix='.py', delete=False) as wrapper:
                         wrapper.write(f'''import sys
@@ -440,6 +444,9 @@ import json
 # Set LEDMATRIX_ROOT
 os.environ['LEDMATRIX_ROOT'] = r"{PROJECT_ROOT}"
 
+# The params, as JSON on this wrapper's own stdin
+params = json.loads(sys.stdin.read())
+
 # Run the script and provide params as JSON via stdin
 proc = subprocess.Popen(
     [sys.executable, r"{script_file}"],
@@ -451,7 +458,6 @@ proc = subprocess.Popen(
 )
 
 # Send params as JSON to stdin
-params = {params_json}
 stdout, _ = proc.communicate(input=json.dumps(params), timeout=120)
 print(stdout)
 sys.exit(proc.returncode)
@@ -461,6 +467,7 @@ sys.exit(proc.returncode)
                     try:
                         result = subprocess.run(
                             ['python3', wrapper_path],
+                            input=params_json,
                             capture_output=True,
                             text=True,
                             timeout=120,