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/conversationNormalization.ts

@@ -0,0 +1,67 @@
+/**
+ * Wire → domain normalization for the conversation transcript read (LS7).
+ *
+ * Mirrors the LS6 backend DTO (`crates/app-tauri/src/dto.rs`): `TurnPageDto`
+ * (camelCase `turns` / `hasMore` / `nextAnchor`), `TurnViewDto`
+ * (`id` / `atMs` / `role` / `source` / `text` / `textLen`) and the serde-tagged
+ * `TurnSourceDto` (`{ kind: "human" }` | `{ kind: "agent", agentId }`). The
+ * `source` mapping is calqued on `workStateNormalization.ts`.
+ */
+
+import type { TurnPage, TurnRole, TurnSource, TurnView } from "@/domain";
+
+type RecordLike = Record<string, unknown>;
+
+function isRecord(value: unknown): value is RecordLike {
+  return value !== null && typeof value === "object" && !Array.isArray(value);
+}
+
+function stringValue(value: unknown, fallback = ""): string {
+  return typeof value === "string" ? value : fallback;
+}
+
+function numberValue(value: unknown, fallback = 0): number {
+  return typeof value === "number" && Number.isFinite(value) ? value : fallback;
+}
+
+function arrayValue(value: unknown): unknown[] {
+  return Array.isArray(value) ? value : [];
+}
+
+/** Mirror of LS6 `TurnSourceDto` (serde tag `kind`, camelCase `agentId`). */
+function normalizeSource(value: unknown): TurnSource {
+  if (!isRecord(value)) return { kind: "human" };
+  if (value.kind === "agent") {
+    return { kind: "agent", agentId: stringValue(value.agentId, "unknown") };
+  }
+  return { kind: "human" };
+}
+
+/** Mirror of the camelCase-serialized `TurnRole` (`prompt`/`response`/`toolActivity`). */
+function normalizeRole(value: unknown): TurnRole {
+  return value === "response" || value === "toolActivity" ? value : "prompt";
+}
+
+function normalizeTurn(value: unknown, index: number): TurnView {
+  const turn = isRecord(value) ? value : {};
+  const text = stringValue(turn.text);
+  return {
+    id: stringValue(turn.id, `turn-${index}`),
+    atMs: numberValue(turn.atMs, index),
+    role: normalizeRole(turn.role),
+    source: normalizeSource(turn.source),
+    text,
+    textLen: numberValue(turn.textLen, text.length),
+  };
+}
+
+/** Maps a raw `TurnPageDto` payload to the domain {@link TurnPage}. */
+export function normalizeTurnPage(value: unknown): TurnPage {
+  const page = isRecord(value) ? value : {};
+  const nextAnchor = page.nextAnchor;
+  return {
+    turns: arrayValue(page.turns).map(normalizeTurn),
+    hasMore: page.hasMore === true,
+    ...(typeof nextAnchor === "string" ? { nextAnchor } : {}),
+  };
+}