refactor: Agent-Auswahl in Session-Form als Card + Picker-Modal

- buildAgentCard() Helper in ui.js erstellt (wiederverwendbar für Dashboard + Picker)
- Session-Form: select-Dropdown durch klickbare Agent-Card ersetzt
- Agent-Picker-Modal zeigt alle Agents mit identischen Cards wie am Dashboard
- Dashboard refactored: nutzt buildAgentCard() statt dupliziertem Inline-HTML
- Kein duplizierter Code mehr für Agent-Card-Rendering (Badges, Skills, Avatar)

wwwroot/css/form.css

@@ -297,6 +297,104 @@ label.skill-item {
   margin-left: auto;
 }
 
+/* ── Agent Select Card (in Session-Formular) ── */
+
+.agent-select-card {
+  display: flex;
+  align-items: center;
+  gap: var(--box-spacing);
+  padding: var(--box-padding);
+  background: var(--f3-bg);
+  border: var(--border-width) solid var(--f3-border);
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  transition: border-color var(--transition-duration);
+}
+
+.agent-select-card:hover {
+  border-color: var(--primary);
+}
+
+.agent-select-card .card-image {
+  flex: 0 0 4em;
+  height: 4em;
+}
+
+.agent-select-empty {
+  opacity: var(--semi-transparent);
+  display: flex;
+  align-items: center;
+  gap: var(--badge-spacing);
+}
+
+.agent-select-change {
+  margin-left: auto;
+  opacity: var(--semi-transparent);
+  flex-shrink: 0;
+  transition: opacity var(--transition-duration);
+}
+
+.agent-select-card:hover .agent-select-change {
+  opacity: 1;
+  color: var(--primary);
+}
+
+/* ── Agent Picker Modal ── */
+
+.agent-picker-overlay {
+  position: fixed;
+  inset: 0;
+  background: rgb(from var(--f1-bg) r g b / var(--semi-transparent));
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 1000;
+}
+
+.agent-picker-modal {
+  background: var(--f2-bg);
+  border: var(--border-width) solid var(--f2-border);
+  border-radius: var(--border-radius);
+  width: 90vw;
+  max-width: var(--modal-width);
+  max-height: 80vh;
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+}
+
+.agent-picker-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: var(--box-padding);
+  border-bottom: var(--border-width) solid var(--f1-border);
+  background: var(--f1-bg);
+  font-weight: bold;
+}
+
+.agent-picker-body {
+  padding: var(--badge-spacing);
+  overflow-y: auto;
+  display: flex;
+  flex-direction: column;
+  gap: var(--badge-spacing);
+}
+
+.agent-picker-item {
+  cursor: pointer;
+  transition: border-color var(--transition-duration), filter var(--transition-duration);
+}
+
+.agent-picker-item:hover {
+  border-color: var(--primary);
+  filter: var(--hover-filter);
+}
+
+.agent-picker-item.selected {
+  border-color: var(--primary);
+}
+
 /* ── Profile ── */
 
 .profile-message {