Refactor the yaml data package to group data sources by category

docs/internal/prompt-input.md

@@ -24,7 +24,8 @@ Inputs:
 Outputs:
 
 - `promptinput.Package` with schema version, RunID, report metadata, named
-  module stanzas, Recent Changes, and source warnings
+  module stanzas grouped for prompt presentation, Recent Changes, and source
+  warnings
 - YAML bytes from `promptinput.MarshalYAML`
 - YAML file written atomically by `promptinput.Save`
 
@@ -38,15 +39,37 @@ report:
   prompt_id: <prompt_id>
 briefing:
   metadata: {}
-  current_conditions: {}
-  narrative_forecast: {}
-  hourly_forecast: {}
+  applicable_risk_products:
+    alert_digest: {}
+  derived_summaries:
+    derived_daily_summary: {}
+    derived_daypart_summaries: {}
+    precip_timing: {}
+    outdoor_windows: {}
+  narrative_products:
+    narrative_forecast: {}
+    area_forecast_discussion: {}
+    weather_story: {}
+  raw_data:
+    current_conditions: {}
+    hourly_forecast: {}
 recent_changes:
   items: []
 ```
 
-The `briefing` mapping contains named module stanzas. Stanza order follows the
-module snapshot output order.
+The `briefing` mapping keeps `metadata` directly under `briefing` and groups
+weather module stanzas under prompt-facing categories. This grouping is a YAML
+presentation concern only: module snapshots remain flat, and loaded
+`promptinput.Package` values expose flat stanza names in `Briefing.Values`.
+Within each category, stanza order follows the module snapshot output order.
+
+Current categories are:
+
+- `applicable_risk_products`: location-applicable alerts, warnings, outlooks,
+  discussions, and similar risk products.
+- `derived_summaries`: deterministic summaries and calculated report facts.
+- `narrative_products`: official narrative text products and forecast stories.
+- `raw_data`: minimally transformed underlying weather data.
 
 ## Boundaries
 
@@ -92,6 +115,7 @@ Inspect:
 ## Invariants
 
 - Scriptorium receives structured YAML through `--input data_package=<path>`.
-- Module stanza order is deterministic for generated snapshots.
+- Module stanza order is deterministic within each prompt-facing category.
+- Every non-metadata module stanza has exactly one prompt-input category.
 - Recent Changes are provided by `internal/changes`; this package does not
   infer changes from rendered report text.