feat(frontend): viewer humain fil-par-paire en lecture seule (LS7)

Frontend pur, lecture seule, consomme read_conversation_page (LS6) ; aucun changement backend.
- adapters : conversation.ts (gateway) + conversationNormalization.ts.
- features/conversations : useConversationThread, ConversationViewer, index.
- domain (types LS7), ports (port + Gateways.conversation), adapters/index, mock (+ clé inventaire).
- features/workstate : ProjectWorkStatePanel prop onOpenConversation.
- features/projects : ProjectsView swap viewer.
- tests (QA, verts) : conversationNormalization, mock/conversationGateway,
  useConversationThread, ConversationViewer, ProjectsView.ls7. tsc 0, vitest 443/443 (+36).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/adapters/index.ts

@@ -26,6 +26,7 @@ import { TauriEmbedderGateway } from "./embedder";
 import { TauriGitGateway } from "./git";
 import { TauriPermissionGateway } from "./permission";
 import { TauriWorkStateGateway } from "./workState";
+import { TauriConversationGateway } from "./conversation";
 
 function notImplemented(what: string): never {
   const err: GatewayError = {
@@ -59,6 +60,7 @@ export function createTauriGateways(): Gateways {
     embedder: new TauriEmbedderGateway(),
     permission: new TauriPermissionGateway(),
     workState: new TauriWorkStateGateway(),
+    conversation: new TauriConversationGateway(),
   };
 }
 
@@ -77,4 +79,5 @@ export {
   TauriGitGateway,
   TauriPermissionGateway,
   TauriWorkStateGateway,
+  TauriConversationGateway,
 };