Document commute provider seam for personal report

OpenJibo/docs/calendar-architecture.md

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+# Calendar Architecture
+
+Pegasus treated calendar as a loop-scoped report surface, with report output fed by the
+household context instead of an isolated generic calendar service.
+
+In OpenJibo, the current calendar path follows the same broad shape:
+
+- calendar report output is loop-scoped
+- the report provider can read persisted loop calendar events
+- birthday and other personal dates already live in the loop-scoped holiday list
+- the personal report merges the report provider output into the spoken flow
+
+Current behavior:
+
+- if loop calendar events exist, the provider surfaces the next matching items
+- if no loop calendar events exist, the provider falls back to the merged holiday list
+- birthdays and custom holiday entries can therefore appear in the calendar section
+- the personal report still degrades safely when no calendar data is available
+
+Notes:
+
+- the current provider is intentionally lightweight and in-process
+- this gives us a swappable seam for later Azure-backed calendar sync
+- commute remains a separate report gap for the next pass