20260901T1732Z architecture changed source reconciliation

What. Added the Changed-source reconciliation section to the architecture doc: source version supersession, event revision, extraction keyed by (event, revision, extractor_version), the diff outcomes (keep / supersede / new), partial alignment by identifying hard claims, and the orthogonality to extractor_version re-runs. Source and Event concept definitions and the module 1/2 ownership rows updated to match.

Why. D11 settled the semantics of a changed-source re-ingest (PRD I4) but owed the mechanics to the architecture doc; nothing there described them.

Verify. Read the section against D11 and I4's acceptance criterion: a rescheduled calendar event yields one event, re-extracted, with the removed attendee's claims superseded and no duplicate members.