feat(PROJ-17): Admin Dashboard Systemauslastung immer anzeigen

- Systemauslastungs-Sektion wird immer gerendert (nicht nur bei Erfolg)
- Fehlermeldung wenn /api/admin/system/stats nicht erreichbar ist
- Feature-Status auf In Review gesetzt

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

internal/index/xapian.go

@@ -0,0 +1,126 @@
+//go:build xapian
+
+package index
+
+/*
+#cgo pkg-config: xapian-core
+#cgo LDFLAGS: -lstdc++
+#include "xapian_wrapper.h"
+#include <stdlib.h>
+*/
+import "C"
+import (
+	"encoding/json"
+	"fmt"
+	"unsafe"
+)
+
+type xapianIndex struct {
+	db *C.XapianDB
+}
+
+func newXapian(dir string) (Indexer, error) {
+	cdir := C.CString(dir)
+	defer C.free(unsafe.Pointer(cdir))
+	var cerr *C.char
+	db := C.xapian_open(cdir, 1, &cerr)
+	if db == nil {
+		msg := C.GoString(cerr)
+		C.xapian_free_string(cerr)
+		return nil, fmt.Errorf("xapian open: %s", msg)
+	}
+	return &xapianIndex{db: db}, nil
+}
+
+func (x *xapianIndex) IndexSync(doc MailDocument) error {
+	cid := C.CString(doc.ID)
+	defer C.free(unsafe.Pointer(cid))
+	cfrom := C.CString(doc.From)
+	defer C.free(unsafe.Pointer(cfrom))
+	cto := C.CString(doc.To)
+	defer C.free(unsafe.Pointer(cto))
+	csubj := C.CString(doc.Subject)
+	defer C.free(unsafe.Pointer(csubj))
+	cbody := C.CString(doc.Body)
+	defer C.free(unsafe.Pointer(cbody))
+	var cerr *C.char
+	rc := C.xapian_index(x.db, cid, cfrom, cto, csubj, cbody, C.longlong(doc.Date.Unix()), &cerr)
+	if rc != 0 {
+		msg := C.GoString(cerr)
+		C.xapian_free_string(cerr)
+		return fmt.Errorf("xapian index: %s", msg)
+	}
+	return nil
+}
+
+func (x *xapianIndex) Delete(id string) error {
+	cid := C.CString(id)
+	defer C.free(unsafe.Pointer(cid))
+	var cerr *C.char
+	rc := C.xapian_delete(x.db, cid, &cerr)
+	if rc != 0 {
+		msg := C.GoString(cerr)
+		C.xapian_free_string(cerr)
+		return fmt.Errorf("xapian delete: %s", msg)
+	}
+	return nil
+}
+
+func (x *xapianIndex) Search(req SearchRequest) (*SearchResult, error) {
+	cquery := C.CString(req.Query)
+	defer C.free(unsafe.Pointer(cquery))
+	cfrom := C.CString(req.From)
+	defer C.free(unsafe.Pointer(cfrom))
+	cown := C.CString(req.OwnEmail)
+	defer C.free(unsafe.Pointer(cown))
+	cto := C.CString(req.To)
+	defer C.free(unsafe.Pointer(cto))
+
+	var dateFrom, dateTo C.longlong
+	if req.DateFrom != nil {
+		dateFrom = C.longlong(req.DateFrom.Unix())
+	}
+	if req.DateTo != nil {
+		dateTo = C.longlong(req.DateTo.Unix())
+	}
+	page := req.Page
+	if page < 1 {
+		page = 1
+	}
+	offset := C.int((page - 1) * req.PageSize)
+	limit := C.int(req.PageSize)
+	if limit <= 0 {
+		limit = 25
+	}
+
+	var cerr *C.char
+	cresult := C.xapian_search(x.db, cquery, cfrom, cown, cto, dateFrom, dateTo, offset, limit, &cerr)
+	if cresult == nil {
+		msg := C.GoString(cerr)
+		C.xapian_free_string(cerr)
+		return nil, fmt.Errorf("xapian search: %s", msg)
+	}
+	defer C.xapian_free_string(cresult)
+	jsonStr := C.GoString(cresult)
+
+	var raw struct {
+		Total int `json:"total"`
+		Hits  []struct {
+			ID    string  `json:"id"`
+			Score float64 `json:"score"`
+		} `json:"hits"`
+	}
+	if err := json.Unmarshal([]byte(jsonStr), &raw); err != nil {
+		return nil, fmt.Errorf("xapian parse result: %w", err)
+	}
+	hits := make([]Hit, len(raw.Hits))
+	for i, h := range raw.Hits {
+		hits[i] = Hit{ID: h.ID, Score: h.Score}
+	}
+	return &SearchResult{Total: raw.Total, Hits: hits}, nil
+}
+
+func (x *xapianIndex) Close() error {
+	C.xapian_close(x.db)
+	return nil
+}