Add Weekend Outlook generation

docs/internal/changes.md

@@ -37,7 +37,7 @@ The app maps these config fields into comparison thresholds:
 
 ## Behavior
 
-Daily and 3-Day comparison currently detect:
+Daily, 3-Day, and Weekend comparison currently detect:
 
 - temperature changes crossing configured thresholds
 - precipitation probability and timing changes
@@ -48,12 +48,15 @@ Daily and 3-Day comparison currently detect:
 When no prior comparable snapshot exists, the app sends an empty Recent Changes
 section in the data package. Daily Today and Daily Tomorrow are compatible for
 same-valid-date comparison through the report registry. 3-Day Outlook compares
-with prior 3-Day Outlook snapshots for the same valid local date.
+with prior 3-Day Outlook snapshots for the same valid local date. Weekend
+Outlook compares with prior Weekend Outlook snapshots for the same weekend
+window.
 
 ## Failure Behavior
 
 Daily comparison requires both inputs to contain Daily briefing content. 3-Day
-comparison requires both inputs to contain 3-Day briefing content.
+comparison requires both inputs to contain 3-Day briefing content. Weekend
+comparison requires both inputs to contain Weekend briefing content.
 
 ## Tests
 
@@ -61,6 +64,7 @@ Inspect:
 
 - `internal/changes/daily_test.go`
 - `internal/changes/three_day_test.go`
+- `internal/changes/weekend_test.go`
 - `internal/app/app_test.go`
 
 ## Invariants