feat(PROJ-44): Snippet + match_field fuer Suche, GetAttachmentText

Hit-Struct um Snippet + MatchField erweitert. enrichHitsWithSnippets
fuellt diese pro Treffer: detectMatchField probt subject>body>
attachment_text>attachment_names>from_addr>to_addr; buildSnippet ruft
CALL SNIPPETS mit <b>-Markern. Snippet-Fehler droppen den Treffer nicht.

AttachmentTextReader-Interface + Manticore-Implementation
GetAttachmentText liefert den indexierten OCR-Text fuer den neuen
/ocr-text-Endpoint.

internal/index/index.go

@@ -35,9 +35,16 @@ type SearchRequest struct {
 }
 
 // Hit is a single search result.
+//
+// PROJ-44: Snippet and MatchField are populated by the Manticore Search path
+// when a full-text query was provided. They remain empty for filter-only
+// searches (e.g. date range without query) and when the per-hit highlight
+// pass fails — the hit is still returned in that case (no hard error).
 type Hit struct {
-	ID    string  `json:"id"`
-	Score float64 `json:"score"`
+	ID         string  `json:"id"`
+	Score      float64 `json:"score"`
+	Snippet    string  `json:"snippet,omitempty"`     // HTML-marked excerpt with <b>match</b> tags
+	MatchField string  `json:"match_field,omitempty"` // subject|body|attachment_text|attachment_names|from_addr|to_addr
 }
 
 // SearchResult holds paginated search results.
@@ -63,6 +70,14 @@ type AttachmentTextUpdater interface {
 	UpdateAttachmentText(mailID, text string) error
 }
 
+// AttachmentTextReader is implemented by indexers that can return the stored
+// OCR-extracted attachment text for a mail. Optional add-on to Indexer.
+//
+// PROJ-44: Manticore implements this for the /api/mails/{id}/ocr-text endpoint.
+type AttachmentTextReader interface {
+	GetAttachmentText(mailID string) (string, error)
+}
+
 // TenantIndexer manages per-tenant Indexer instances.
 // Implemented by ManticoreTenantManager (primary) and TenantIndexManager (legacy Xapian).
 type TenantIndexer interface {