docs: fix advisory items in date integration plan

Author: johnleider

docs/superpowers/plans/2026-03-26-v0-date-integration.md

@@ -262,7 +262,7 @@ export class LegacyDateAdapterCompat<T> implements DateAdapter<T> {
   }
 
   endOfWeek (date: T): T {
-    return this.legacy.endOfWeek(date, this.firstDayOfWeek)
+    return this.legacy.endOfWeek(date)
   }
 
   getWeekArray (date: T): T[][] {
@@ -850,7 +850,7 @@ The default adapter now uses `Temporal.PlainDateTime` instead of native `Date`.
 Custom adapters must implement v0's `DateAdapter<T>` interface. Key changes:
 
 - `firstDayOfWeek` is now an adapter property, not a method parameter
-- 5 method signatures updated (startOfWeek, getWeekArray, getWeekdays, getWeek, endOfWeek)
+- 4 method signatures updated (startOfWeek, getWeekArray, getWeekdays, getWeek) + `firstDayOfWeek` is now an adapter property
 - Old adapters are auto-detected and wrapped with a deprecation warning
 
 #### Third-party adapters