feat(chat): conversations persistantes + mémoire multi-tour (v0.36.0)

Store SQLite conversations/messages (propriété par actor, fenêtre 20),
historique rejoué au LLM (runAgentTurn history), ChatService persiste et
renvoie conversationId. API GET/DELETE /conversations + chat avec
conversationId. UI Chat: sidebar conversations (drawer mobile), nouvelle,
reprise, suppression. docs/conversations.md. 83 tests verts, build web vert.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016w5jRe87MGdd6AMvXQcHNi

web/src/api.ts

@@ -14,6 +14,19 @@ export interface Asset {
   docLink: string | null;
 }
 
+export interface ConversationMeta {
+  id: string;
+  title: string;
+  createdAt: number;
+  updatedAt: number;
+}
+
+export interface ChatMessage {
+  role: "user" | "assistant";
+  content: string;
+  ts: number;
+}
+
 export class ApiError extends Error {
   constructor(
     public status: number,
@@ -41,12 +54,21 @@ export const api = {
       body: JSON.stringify({ user, password, totp }),
     }),
 
-  chat: (token: string, message: string) =>
-    req<{ reply: string }>("/chat", token, {
+  chat: (token: string, message: string, conversationId?: string | null) =>
+    req<{ reply: string; conversationId: string | null }>("/chat", token, {
       method: "POST",
-      body: JSON.stringify({ message }),
+      body: JSON.stringify({ message, conversationId: conversationId ?? undefined }),
     }),
 
+  conversations: (token: string) =>
+    req<{ conversations: ConversationMeta[] }>("/conversations", token),
+
+  conversation: (token: string, id: string) =>
+    req<{ messages: ChatMessage[] }>(`/conversations/${encodeURIComponent(id)}`, token),
+
+  deleteConversation: (token: string, id: string) =>
+    req<{ ok: boolean }>(`/conversations/${encodeURIComponent(id)}`, token, { method: "DELETE" }),
+
   review: (token: string) => req<{ assets: Asset[] }>("/review", token),
 
   approve: (token: string, id: string) =>