feat(search): add SearchMatchData record for per-document match signals

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

backend/src/main/java/org/raddatz/familienarchiv/dto/SearchMatchData.java

@@ -0,0 +1,48 @@
+package org.raddatz.familienarchiv.dto;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import java.util.List;
+import java.util.UUID;
+
+/**
+ * Match signals for a single document in a full-text search result.
+ * All fields are non-null except {@code transcriptionSnippet}, which is null
+ * when no transcription block matched the query.
+ */
+public record SearchMatchData(
+        /**
+         * Best-ranked matching transcription line, or null if no block matched.
+         */
+        String transcriptionSnippet,
+
+        /**
+         * Character offsets of highlighted terms within the document title.
+         * Empty when the title did not contribute to the match.
+         */
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        List<MatchOffset> titleOffsets,
+
+        /**
+         * True when the sender's name matched the query.
+         */
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        boolean senderMatched,
+
+        /**
+         * IDs of receiver persons whose names matched the query.
+         */
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        List<UUID> matchedReceiverIds,
+
+        /**
+         * IDs of tags whose names matched the query.
+         */
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        List<UUID> matchedTagIds
+) {
+    /** Canonical "no match data" value for a single document. */
+    public static SearchMatchData empty() {
+        return new SearchMatchData(null, List.of(), false, List.of(), List.of());
+    }
+}