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/ports/index.ts

@@ -31,6 +31,7 @@ import type {
   MemoryType,
   EffectivePermissions,
   PermissionSet,
+  PageDirection,
   Project,
   ProjectPermissions,
   ProjectWorkState,
@@ -40,6 +41,7 @@ import type {
   SkillScope,
   Template,
   TerminalSession,
+  TurnPage,
   Unsubscribe,
 } from "@/domain";
 
@@ -660,6 +662,26 @@ export interface WorkStateGateway {
   getProjectWorkState(projectId: string): Promise<ProjectWorkState>;
 }
 
+/** One paginated page request over a conversation transcript (LS7). */
+export interface ConversationPageRequest {
+  /** Turn id to paginate around; omit to start from a thread end. */
+  anchor?: string;
+  /** Travel direction; defaults to `"backward"` (latest page first). */
+  direction?: PageDirection;
+  /** Requested page size (clamped by the backend to `[1, 200]`). */
+  limit?: number;
+}
+
+/** Read-only, paginated access to a conversation's full transcript (LS7). */
+export interface ConversationGateway {
+  /** Reads one page of a conversation's transcript (full text, never truncated). */
+  readPage(
+    projectId: string,
+    conversationId: string,
+    request?: ConversationPageRequest,
+  ): Promise<TurnPage>;
+}
+
 /**
  * The full set of gateways the app depends on, injected via the DI provider.
  * The composition (real vs mock) is chosen in `app/`.
@@ -680,4 +702,5 @@ export interface Gateways {
   embedder: EmbedderGateway;
   permission: PermissionGateway;
   workState: WorkStateGateway;
+  conversation: ConversationGateway;
 }