Add Organization aggregate (client-as-status), wired but inert

Prospect -> Client -> PastClient (Prospect -> PastClient allowed
directly too - a prospect that never converted). "Client" is a status
on Organization, not a separate aggregate, per the event-sourcing
plan's design decision. Wired into the same dispatch points as the
other three aggregates (content.rs's bucket map, answers.rs's
create/transition dispatch) so it's ready the moment content
references an "organizations" bucket - nothing does yet, so this lands
compiled and tested but with zero production surface.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/aggregates/mod.rs

@@ -9,6 +9,7 @@
 #![cfg(feature = "ssr")]
 
 pub mod applicant;
+pub mod organization;
 pub mod project;
 pub mod subscriber;