feat: B2B contact button auto-fills context message

When clicking "Skontaktuj się" on a classified ad, the conversation
now starts with a pre-filled message: "Hej, piszę w sprawie ogłoszenia
na tablicy B2B: „<tytuł>"". If conversation already exists, the
context is pre-filled in the editor for the user to send.

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

static/js/conversations.js

@@ -3161,11 +3161,19 @@
             }
         }
 
-        // If URL has ?new_to=<user_id>, open new message modal with pre-selected recipient
+        // If URL has ?new_to=<user_id>, open or create conversation with that user
         var newToParam = urlParams.get('new_to');
         if (newToParam) {
             var targetUserId = parseInt(newToParam);
             if (targetUserId) {
+                // Build context message if coming from classified/B2B
+                var ctxType = urlParams.get('ctx');
+                var ctxTitle = urlParams.get('ctx_title');
+                var contextMessage = '';
+                if (ctxType === 'classified' && ctxTitle) {
+                    contextMessage = 'Hej, piszę w sprawie ogłoszenia na tablicy B2B: „' + decodeURIComponent(ctxTitle) + '"';
+                }
+
                 // Check if conversation with this user already exists (1:1)
                 var existingConv = state.conversations.find(function (c) {
                     return !c.is_group && c.members && c.members.some(function (m) {
@@ -3174,12 +3182,27 @@
                 });
                 if (existingConv) {
                     ConversationList.selectConversation(existingConv.id);
+                    // Pre-fill editor with context message
+                    if (contextMessage) {
+                        setTimeout(function () {
+                            var editor = document.querySelector('#chatInput .ql-editor, #chatInput');
+                            if (editor) {
+                                if (editor.classList && editor.classList.contains('ql-editor')) {
+                                    editor.innerHTML = '<p>' + contextMessage + '</p>';
+                                } else if (editor.value !== undefined) {
+                                    editor.value = contextMessage;
+                                }
+                            }
+                        }, 800);
+                    }
                 } else {
-                    // Open new message modal — create conversation via API, then open it
+                    // Create conversation via API with optional first message
+                    var payload = { member_ids: [targetUserId] };
+                    if (contextMessage) payload.message = contextMessage;
                     fetch('/api/conversations', {
                         method: 'POST',
                         headers: { 'Content-Type': 'application/json', 'X-CSRFToken': window.__CSRF_TOKEN__ },
-                        body: JSON.stringify({ member_ids: [targetUserId] })
+                        body: JSON.stringify(payload)
                     }).then(function (r) { return r.json(); }).then(function (data) {
                         if (data.id) {
                             window.location.href = '/wiadomosci?conv=' + data.id;

templates/classifieds/view.html

@@ -727,7 +727,7 @@
                     </svg>
                     <span id="interestBtnText">{% if user_interested %}Zainteresowany{% else %}Jestem zainteresowany{% endif %}</span>
                 </button>
-                <a href="{{ url_for('messages.conversations_page') }}?new_to={{ classified.author_id }}" class="btn btn-primary">Skontaktuj sie</a>
+                <a href="{{ url_for('messages.conversations_page') }}?new_to={{ classified.author_id }}&ctx=classified&ctx_title={{ classified.title|urlencode }}" class="btn btn-primary">Skontaktuj sie</a>
             </div>
             {% endif %}
         </div>

templates/messages/conversations.html

@@ -326,7 +326,7 @@ window.__CSRF_TOKEN__ = '{{ csrf_token() }}';
 // Load conversations.js after data is set
 (function() {
     var s = document.createElement('script');
-    s.src = '{{ url_for("static", filename="js/conversations.js") }}?v=26';
+    s.src = '{{ url_for("static", filename="js/conversations.js") }}?v=27';
     document.body.appendChild(s);
 })();
 {% endblock %}