feat: Review-Agent (Multi-Agent-Kommunikation)

- Session hat optionalen ReviewAgentId + MaxReviewIterations
- Nach end_turn des Worker-Agents wird der Review-Agent aufgerufen
- Review-Agent bekommt Worker-Konversation als Kontext + kann Tools nutzen
- [APPROVED] in Review-Antwort → fertig, sonst Feedback an Worker
- Worker korrigiert und wird erneut reviewed (max N Runden)
- SSE-Events: review_start, review_text, review_tool_use, review_feedback, review_approved
- Chat-UI: Review-Phase als eigene Bubble mit Header, Text, Status
- Session-Page: Review-Agent-Picker (gleicher Agent-Card-Helper)
- Dashboard: Review-Agent-Badge auf Session-Cards
- DB-Migration: review_agent_id, max_review_iterations auf sessions

wwwroot/css/chat.css

@@ -973,3 +973,74 @@
   text-align: center;
   padding: var(--page-padding);
 }
+
+/* Review Bubbles */
+
+.review-bubble {
+  align-self: flex-start;
+  background: var(--f1-bg);
+  border: var(--border-width) solid var(--f1-border);
+  border-left: 3px solid var(--secondary);
+  max-width: 80%;
+  display: flex;
+  flex-direction: column;
+  gap: var(--badge-spacing);
+}
+
+.review-header {
+  display: flex;
+  align-items: center;
+  gap: var(--badge-spacing);
+  color: var(--secondary);
+}
+
+.review-round {
+  opacity: var(--semi-transparent);
+  font-size: var(--font-size);
+}
+
+.review-content {
+  word-break: break-word;
+}
+
+.review-tool-use {
+  font-size: var(--font-size);
+  opacity: var(--semi-transparent);
+  display: flex;
+  align-items: center;
+  gap: var(--badge-spacing);
+}
+
+.review-status {
+  display: flex;
+  align-items: center;
+  gap: var(--badge-spacing);
+  padding-top: var(--badge-spacing);
+  border-top: var(--border-width) solid var(--f2-border);
+  font-weight: bold;
+}
+
+.review-approved {
+  color: var(--success);
+}
+
+.review-rejected {
+  color: var(--warning);
+}
+
+/* Review Iterations Row */
+
+.review-iterations-row {
+  display: flex;
+  align-items: center;
+  gap: var(--box-spacing);
+}
+
+.review-iterations-row label {
+  margin: 0;
+  white-space: nowrap;
+}
+
+.review-iterations-row input[type="number"] {
+  width: 5em;
+}