feat(audit): expose commentId on rolled-up activity feed projection

Adds getCommentId() to ActivityFeedRow and selects
(ag.payload->>'commentId')::uuid from findRolledUpActivityFeed so
chronik consumers can build deep-link URLs for COMMENT_ADDED and
MENTION_CREATED events. Null for other kinds.

Refs #300.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/audit/ActivityFeedRow.java

@@ -15,4 +15,6 @@ public interface ActivityFeedRow {
     boolean isYouParticipated();
     int getCount();
     Instant getHappenedAtUntil();
+    /** Present only for COMMENT_ADDED and MENTION_CREATED — null otherwise. */
+    UUID getCommentId();
 }

backend/src/main/java/org/raddatz/familienarchiv/audit/AuditLogQueryRepository.java

@@ -99,7 +99,8 @@ public interface AuditLogQueryRepository extends JpaRepository<AuditLog, UUID> {
                       AND n.reference_id = (ag.payload->>'commentId')::uuid
                 )                                                      AS youParticipated,
                 ag.count                                               AS count,
-                ag.happened_at_until                                   AS happenedAtUntil
+                ag.happened_at_until                                   AS happenedAtUntil,
+                (ag.payload->>'commentId')::uuid                       AS commentId
             FROM aggregated ag
             LEFT JOIN users u ON u.id = ag.actor_id
             ORDER BY ag.happened_at DESC

backend/src/test/java/org/raddatz/familienarchiv/dashboard/AuditLogQueryRepositoryRolledUpTest.java

@@ -271,6 +271,45 @@ class AuditLogQueryRepositoryRolledUpTest {
         );
     }
 
+    @Test
+    void rolledUpFeed_exposes_commentId_for_COMMENT_ADDED_events() {
+        insertUserAndDocs();
+        UUID commentId = UUID.randomUUID();
+        insertAuditEvent(USER_ID, DOC_ID, "COMMENT_ADDED",
+                Instant.parse("2026-04-20T10:00:00Z"), Map.of("commentId", commentId.toString()));
+
+        List<ActivityFeedRow> rows = auditLogQueryRepository.findRolledUpActivityFeed(USER_ID.toString(), 40);
+
+        assertThat(rows).hasSize(1);
+        assertThat(rows.get(0).getCommentId()).isEqualTo(commentId);
+    }
+
+    @Test
+    void rolledUpFeed_exposes_commentId_for_MENTION_CREATED_events() {
+        insertUserAndDocs();
+        UUID commentId = UUID.randomUUID();
+        insertAuditEvent(OTHER_USER_ID, DOC_ID, "MENTION_CREATED",
+                Instant.parse("2026-04-20T10:00:00Z"),
+                Map.of("commentId", commentId.toString(), "mentionedUserId", USER_ID.toString()));
+
+        List<ActivityFeedRow> rows = auditLogQueryRepository.findRolledUpActivityFeed(USER_ID.toString(), 40);
+
+        assertThat(rows).hasSize(1);
+        assertThat(rows.get(0).getCommentId()).isEqualTo(commentId);
+    }
+
+    @Test
+    void rolledUpFeed_commentId_is_null_for_non_comment_kinds() {
+        insertUserAndDocs();
+        insertAuditEvent(USER_ID, DOC_ID, "TEXT_SAVED",
+                Instant.parse("2026-04-20T10:00:00Z"), Map.of("blockId", "ccc", "pageNumber", "1"));
+
+        List<ActivityFeedRow> rows = auditLogQueryRepository.findRolledUpActivityFeed(USER_ID.toString(), 40);
+
+        assertThat(rows).hasSize(1);
+        assertThat(rows.get(0).getCommentId()).isNull();
+    }
+
     @Test
     void youMentioned_is_false_when_mention_created_payload_targets_different_user() {
         insertUserAndDocs();

backend/src/test/java/org/raddatz/familienarchiv/dashboard/DashboardServiceTest.java

@@ -107,6 +107,7 @@ class DashboardServiceTest {
             public boolean isYouParticipated() { return false; }
             public int getCount() { return 1; }
             public Instant getHappenedAtUntil() { return null; }
+            public UUID getCommentId() { return null; }
         };
     }
 }