fix(messages): prevent double message sending on Enter key

- Added _isSending flag to Composer.send() — blocks concurrent sends
- Added Quill keyboard binding override for Enter (handler returns false)
- Added stopImmediatePropagation() to DOM keydown handler
- Added _isCreating flag to NewConversation.send()
- Flags reset in finally blocks to handle errors gracefully

Fixes: messages appearing twice when user presses Enter

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/js/conversations.js

@@ -1203,6 +1203,19 @@
                 placeholder: 'Napisz wiadomość...',
                 modules: {
                     toolbar: [['bold', 'italic'], ['link'], ['clean']],
+                    keyboard: {
+                        bindings: {
+                            enter: {
+                                key: 13,
+                                handler: function() { Composer.send(); return false; }
+                            },
+                            shiftEnter: {
+                                key: 13,
+                                shiftKey: true,
+                                handler: function() { return true; } // Allow newline
+                            }
+                        }
+                    }
                 },
             });
 
@@ -1211,7 +1224,9 @@
                 if (e.key === 'Enter' && !e.shiftKey) {
                     e.preventDefault();
                     e.stopPropagation();
+                    e.stopImmediatePropagation();
                     Composer.send();
+                    return false;
                 }
             });
 
@@ -1254,12 +1269,14 @@
 
         send: async function () {
             if (!state.currentConversationId || !state.quill) return;
+            if (state._isSending) return; // Prevent double send
 
             var html = state.quill.root.innerHTML;
             var text = state.quill.getText().trim();
 
             if (!text && !state.attachedFiles.length) return;
 
+            state._isSending = true;
             var convId = state.currentConversationId;
 
             try {
@@ -1296,6 +1313,8 @@
                 });
             } catch (e) {
                 alert('Nie udało się wysłać wiadomości: ' + e.message);
+            } finally {
+                state._isSending = false;
             }
         },
 
@@ -1963,6 +1982,8 @@
                 alert('Wybierz co najmniej jednego odbiorcę');
                 return;
             }
+            if (state._isCreating) return; // Prevent double send
+            state._isCreating = true;
 
             var messageContent = '';
             if (state.newMessageQuill) {
@@ -2005,6 +2026,8 @@
                 ConversationList.selectConversation(result.id);
             } catch (e) {
                 alert('Nie udało się utworzyć konwersacji: ' + e.message);
+            } finally {
+                state._isCreating = false;
             }
         },
     };