Household context builder with token budget

harness.BuildContext reads the household context in one read transaction:
today and its weekday in the household timezone, Regulars (cuisine, method,
minutes, favorite), the Quest log, the last 60 passed Side quests and the
plans of the last four ISO weeks. A character budget trims the oldest plans
first, then the oldest passes, never Regulars; a budget too small for what
is never trimmed is an error.

Maestro task 2f54cec9-ec41-42af-b8ee-9e24b8c63057

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -159,6 +159,11 @@ automatic** (D-021).
   with the JSON Schema — the contract is always last. The user message comes
   from the skill's input. `checksums.txt` pins every template; changing one
   without a version bump fails the tests.
+- **Household context** (`harness.BuildContext`): layer 3 holds today's date
+  and weekday in the household timezone, the Regulars, the Quest log, the
+  last 60 passed Side quests and the plans of the last four ISO weeks. A
+  character budget trims the oldest plans first, then the oldest passes;
+  Regulars and the Quest log are never trimmed.
 
 ## Recipe grounding