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/orchestration/heartbeat.ts

@@ -4,7 +4,7 @@ import type { AgentRecord, ConnectorRecord } from "@shared/types";
 import type { OrchestrationDependencies } from "./types";
 import type { RunDispatchParams } from "./turn-context";
 import { pickModelForAgent } from "../model-dispatch";
-import { HUMAN_SENDER_ID } from "../message-dispatch";
+import { HUMAN_SENDER_ID } from "../messaging/dispatch";
 
 /**
  * Every reason a heartbeat attempt can be rejected before a run is

src/main/orchestration/initial-user-turn.ts

@@ -18,7 +18,7 @@
 
 import type { AppDatabase } from "../database";
 import type { AgentMessageRecord } from "@shared/types";
-import { HUMAN_SENDER_ID } from "../message-dispatch";
+import { HUMAN_SENDER_ID } from "../messaging/dispatch";
 
 export interface InitialUserTurnDeps {
   db: AppDatabase;

src/main/orchestration/scheduler-housekeeping.ts

@@ -2,7 +2,7 @@ import type { OrchestrationDependencies } from "./types";
 import { sweepStaleReviews } from "../task-quality-gates";
 import type { SweepStaleReviewsDeps } from "../task-quality-gates";
 import { resolveApprovalDecision } from "../approval-policy";
-import { dispatchAgentMessage } from "../message-dispatch";
+import { dispatchAgentMessage } from "../messaging/dispatch";
 
 export function createHousekeepingScheduler(
   deps: OrchestrationDependencies,

src/main/orchestration/turn-context.ts

@@ -11,7 +11,7 @@ import type { AppDatabase } from "../database";
 import type { ProjectedSkill } from "../skill-types";
 import type { ConnectorId, ExecutionMode } from "@shared/types";
 import type { WorkspaceLockMode, EnqueueRunPayload } from "./types";
-import { normalizeCommentsForPrompt } from "../message-normalize";
+import { normalizeCommentsForPrompt } from "../messaging/normalize";
 import { getConnectorModelPolicy, validateConnectorModelSelection } from "../connector-model-policy";
 import { resolveInitialUserTurn } from "./initial-user-turn";