feat: company selector in B2B classifieds form

Users with multiple companies now see a dropdown to choose which company
a B2B classified ad is posted for. Single-company users get a hidden field.
Server-side validates the selected company_id against user's actual memberships.

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

blueprints/community/classifieds/routes.py

@@ -100,9 +100,19 @@ def new():
             # Automatyczne wygaśnięcie po 30 dniach
             expires = datetime.now() + timedelta(days=30)
 
+            from helpers.company_context import get_active_company_id
+            from database import UserCompany
+
+            form_company_id = request.form.get('company_id', type=int) or get_active_company_id()
+            # Validate user has access to this company
+            if form_company_id and not db.query(UserCompany).filter_by(
+                user_id=current_user.id, company_id=form_company_id
+            ).first():
+                form_company_id = current_user.company_id
+
             classified = Classified(
                 author_id=current_user.id,
-                company_id=current_user.company_id,
+                company_id=form_company_id,
                 listing_type=listing_type,
                 category=category,
                 title=title,

templates/classifieds/new.html

@@ -259,6 +259,24 @@
         <form method="POST" action="{{ url_for('classifieds.classifieds_new') }}" enctype="multipart/form-data">
             <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
 
+            {% if has_multiple_companies %}
+            <div class="form-group">
+                <label for="company_id">Ogłoszenie w imieniu firmy</label>
+                <select id="company_id" name="company_id" class="form-control" style="border: 2px solid var(--primary); background: var(--bg-secondary);">
+                    {% for uc in user_companies %}
+                    {% if uc.company %}
+                    <option value="{{ uc.company_id }}" {% if uc.company_id == active_company_id %}selected{% endif %}>
+                        {{ uc.company.name }}{% if uc.company_id == active_company_id %} (aktywna){% endif %}
+                    </option>
+                    {% endif %}
+                    {% endfor %}
+                </select>
+                <small style="color: var(--text-secondary); margin-top: 4px; display: block;">Ogłoszenie będzie widoczne na profilu wybranej firmy</small>
+            </div>
+            {% else %}
+            <input type="hidden" name="company_id" value="{{ active_company_id }}">
+            {% endif %}
+
             <div class="form-group">
                 <label>Typ ogłoszenia *</label>
                 <div class="type-selector">