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/conversation.ts

@@ -0,0 +1,42 @@
+/**
+ * Tauri adapter for {@link ConversationGateway} (LS7 human transcript viewer).
+ *
+ * This is the only frontend place that knows the `read_conversation_page`
+ * command name and its argument shape; features consume the gateway port
+ * through DI.
+ *
+ * **Wire contract (verified against LS6 — `crates/app-tauri/src/commands.rs`
+ * + `dto.rs`):** the command takes a *single* `request` argument deserialized
+ * into `ReadConversationPageRequestDto` (`#[serde(rename_all = "camelCase")]`)
+ * with flat fields `projectId`, `conversationId`, `anchor` (optional turn id),
+ * `direction` (`"forward"`/`"backward"`, default backward) and `limit`
+ * (optional, `0`/omit ⇒ default 50, clamped to `[1, 200]`). It returns a
+ * `TurnPageDto` (`turns` / `hasMore` / `nextAnchor`). Note: there is **no**
+ * nested `cursor` object on the wire — the backend builds the domain
+ * `PageCursor` itself from the flat `anchor`/`direction` fields.
+ */
+
+import { invoke } from "@tauri-apps/api/core";
+
+import type { TurnPage } from "@/domain";
+import type { ConversationGateway, ConversationPageRequest } from "@/ports";
+import { normalizeTurnPage } from "./conversationNormalization";
+
+export class TauriConversationGateway implements ConversationGateway {
+  async readPage(
+    projectId: string,
+    conversationId: string,
+    request?: ConversationPageRequest,
+  ): Promise<TurnPage> {
+    const page = await invoke<unknown>("read_conversation_page", {
+      request: {
+        projectId,
+        conversationId,
+        anchor: request?.anchor,
+        direction: request?.direction ?? "backward",
+        limit: request?.limit,
+      },
+    });
+    return normalizeTurnPage(page);
+  }
+}