Add Weekend Outlook generation

docs/internal/briefing.md

@@ -6,7 +6,7 @@ This document describes the implemented briefing package boundary.
 
 `internal/briefing` builds structured report-specific briefing packages from
 forecast summaries and report metadata. The package currently implements Daily
-Today, Daily Tomorrow, and 3-Day Outlook briefing content.
+Today, Daily Tomorrow, 3-Day Outlook, and Weekend Outlook briefing content.
 
 ## Inputs and Outputs
 
@@ -42,6 +42,9 @@ Output:
   character, temperature range, precipitation, wind, risk, outdoor-window, and
   alert inputs, plus broader discussion and weather-story context when
   available.
+- Weekend content uses the same daily outlook summaries and adds planning
+  inputs for best outdoor windows, worst weather windows, rain/storm timing,
+  comfort concerns, and confidence or uncertainty context.
 - Briefing JSON is written atomically by `briefing.Save`.
 
 ## Failure Behavior
@@ -50,6 +53,8 @@ Output:
   daily forecast summary.
 - 3-Day briefing construction requires a 3-Day report definition and at least
   one derived daily summary in the outlook period.
+- Weekend briefing construction requires a Weekend report definition and at
+  least one derived daily summary in the weekend period.
 - Save failures include path and operation context.
 
 ## Tests
@@ -58,6 +63,7 @@ Inspect:
 
 - `internal/briefing/daily_test.go`
 - `internal/briefing/three_day_test.go`
+- `internal/briefing/weekend_test.go`
 - `internal/app/app_test.go`
 - `internal/cli/root_test.go`