fix(config): use correct plugin ID key in secrets template (#275)

The secrets template used "weather" as the key, but the weather plugin's
ID is "ledmatrix-weather". Since ConfigManager deep-merges secrets into
the main config by key, secrets under "weather" never reached the plugin
config at config["ledmatrix-weather"], making the API key invisible to
the plugin.

Co-authored-by: 5ymb01 <5ymb01@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

config/config_secrets.template.json

@@ -1,5 +1,5 @@
 {
-    "weather": {
+    "ledmatrix-weather": {
         "api_key": "YOUR_OPENWEATHERMAP_API_KEY"
     },
     "youtube": {