add conversation delete with confirm

- DELETE /chat/conversations/{id} removes caller from ConversationMember
- ✕ button on each DM in sidebar calls deleteConversation()
- Clicking delete shows browser confirm dialog, then removes conversation
- If the deleted conversation is currently open, resets to empty state
- Clears msgCache for that conversation

src/chat.py

@@ -81,6 +81,19 @@ def list_conversations(request: Request, db: Session = Depends(get_db)):
     result.sort(key=lambda x: x["last_message_at"] or "", reverse=True)
     return result
 
+@router.delete("/conversations/{conversation_id}")
+def delete_conversation(conversation_id: int, request: Request, db: Session = Depends(get_db)):
+    me = get_current_user_from_header(request, db)
+    membership = db.query(ConversationMember).filter(
+        ConversationMember.conversation_id == conversation_id,
+        ConversationMember.user_id == me.id
+    ).first()
+    if not membership:
+        raise HTTPException(status_code=404, detail="Conversation not found")
+    db.delete(membership)
+    db.commit()
+    return {"ok": True}
+
 # ─── Groups ───────────────────────────────────────────────────────────────────
 
 class CreateGroupRequest(BaseModel):

src/static/app.js

@@ -743,6 +743,25 @@ function filterChats() {
   renderChatList();
 }
 
+async function deleteConversation(convId, event) {
+  if (event) { event.stopPropagation(); }
+  if (!confirm("Delete this conversation?")) return;
+  try {
+    await apiFetch(`/chat/conversations/${convId}`, token, "DELETE");
+    if (currentChat && currentChat.type === "dm" && currentChat.id === convId) {
+      currentChat = null;
+      document.getElementById("chat-window").classList.add("hidden");
+      document.getElementById("chat-window").classList.remove("flex");
+      document.getElementById("empty-state").classList.remove("hidden");
+      document.getElementById("call-btn").classList.add("hidden");
+    }
+    delete msgCache[convId];
+    await loadChats();
+  } catch (e) {
+    console.error("deleteConversation error:", e);
+  }
+}
+
 function renderChatList() {
   const q = document.getElementById("sidebar-search").value.toLowerCase();
   const list = document.getElementById("chat-list");
@@ -765,6 +784,7 @@ function renderChatList() {
           <p class="text-xs text-gray-500 truncate">@${conv.other_user.username}</p>
         </div>
         ${conv.unread_count > 0 ? `<span class="w-5 h-5 rounded-full unread-badge text-white text-xs flex items-center justify-center font-medium">${conv.unread_count}</span>` : ""}
+        <button onclick="deleteConversation(${conv.id}, event)" class="shrink-0 w-6 h-6 rounded-lg text-gray-600 hover:text-red-400 hover:bg-white/10 flex items-center justify-center text-xs transition-colors" title="Delete conversation">✕</button>
       `;
       list.appendChild(div);
     });