Move message-*.ts into messaging/ subdir (N10)

Consolidate the two runtime messaging modules under src/main/messaging/. Storage stays in database/messages.ts — that is the SQL layer and belongs with the other DB modules; messaging/ covers the dispatch/normalize runtime around it.

- message-dispatch.ts -> messaging/dispatch.ts
- message-normalize.ts -> messaging/normalize.ts
- add messaging/index.ts barrel for future consumers (existing call sites import the concrete module path directly)
- 10 call sites updated across src/main and tests

src/main/agent-runtime/inbox-projection.ts

@@ -23,7 +23,7 @@ export interface AgentDirectory {
 
 /**
  * Strip control characters (except newlines/tabs) and collapse excessive
- * whitespace runs. Mirrors `message-normalize.ts#cleanText` to keep the
+ * whitespace runs. Mirrors `messaging/normalize.ts#cleanText` to keep the
  * transcript resilient against garbage from upstream senders.
  */
 function cleanText(text: string): string {