feat(08-02): render additional work sections and Sonstiges in form

- Added render_additional_work_sections() method to loop through all sections
- Added render_additional_work_section() to render individual sections with correct field types
- Added render_sonstiges_field() for free text textarea
- Added get_field_key() helper to generate field keys from field names
- Field types: checkbox, abbau_aufbau (radio), checkbox_anzahl, text
- All fields use additional_work[section][key] naming pattern
- Added CSS styling for additional work sections and Sonstiges textarea

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/css/form.css

@@ -323,3 +323,39 @@
 .umzugsliste-wrapper .captcha-widget {
 	margin-bottom: 1rem;
 }
+
+/* Additional Work Sections */
+.umzugsliste-wrapper .additional-work-section {
+	margin-bottom: 1.25rem;
+	padding: 0 0.9375rem;
+}
+
+.umzugsliste-wrapper .additional-work-section .row {
+	margin-bottom: 0.5rem;
+	align-items: center;
+}
+
+.umzugsliste-wrapper .additional-work-section input[type="checkbox"] {
+	margin-right: 0.5rem;
+}
+
+.umzugsliste-wrapper .additional-work-section input[type="text"] {
+	margin-bottom: 0;
+	height: 2rem;
+}
+
+.umzugsliste-wrapper .additional-work-section label {
+	display: inline;
+	margin-bottom: 0;
+}
+
+/* Sonstiges */
+.umzugsliste-wrapper .sonstiges-textarea {
+	width: 100%;
+	padding: 0.5rem;
+	border: 1px solid #ccc;
+	font-size: 0.875rem;
+	margin-bottom: 1rem;
+	resize: vertical;
+	min-height: 100px;
+}