Add canonical audio preparation and meeting context support

docs/meeting-context.md

@@ -107,8 +107,10 @@ or aliases are corrected.
 
 `department`: Organizational unit. Optional and nullable.
 
-`attendance_status`: `present` for participants. This distinguishes attendees
-from mentioned people.
+`attendance_status`: exactly `present` for participants or `mentioned_only` for
+people who are relevant but did not attend. For backward compatibility, a
+missing status defaults to `present` in `participants` and `mentioned_only` in
+`mentioned_people`.
 
 `mentioned_people`: People discussed or referenced but not present. They are
 not participants and must not be treated as speakers.
@@ -153,7 +155,7 @@ mentioned_people:
     aliases: []
     role: null
     department: null
-    attendance_status: "not_present"
+    attendance_status: "mentioned_only"
     notes: "Wurde erwaehnt, war aber nicht anwesend."
 
 organization:
@@ -282,6 +284,8 @@ The current validator checks that:
 - participant ids and mentioned-person ids do not collide
 - referenced departments exist in `organization.departments`
 - `attendance_status` values are valid
+- speaker mappings reference present participants only; mentioned-only people
+  cannot be diarized speakers
 - participants are marked `present`
 - mentioned people are not marked `present`