Add SPC convective discussion briefing module

docs/internal/module.md

@@ -39,6 +39,7 @@ The registry recognizes these IDs:
 - `alert_digest`
 - `spc_convective_outlooks`
 - `area_forecast_discussion`
+- `spc_convective_discussion`
 - `weather_story`
 - `outdoor_windows`
 - `tomorrow_planning`
@@ -46,10 +47,6 @@ The registry recognizes these IDs:
 Every registered module has a builder. Report composition entries that refer to
 unknown or unimplemented module IDs fail validation instead of being skipped.
 
-The package also defines the `spc_convective_discussion` ID and empty option
-struct for the collected contract. It is not a registered module in the
-briefing registry until its builder exists.
-
 ## Options
 
 Most modules use an empty options struct. `area_forecast_discussion` accepts: