Update Group Messaging wiki pages for v1.9.1 multi-layer duress + shard distribution The technical and overview pages still described the pre-Bug-73 binary real/duress member-list model (realMemberSlots/duressMemberSlots only) and didn't document the per-recipient vault shard distribution feature added in v1.9.1 (RecipientPayload's shardOperations/custodyManifest/expectedShards/ shardMetadataAttempted, the ShardPadding tiering scheme, and the fallback stripping on both send and receive).
Add group messaging wiki pages