feat: add development-only synthetic Bell events (#18)

Bell/server/testdata/events/danger-zone.json

@@ -0,0 +1 @@
+{"name":"danger-zone","label":"危险区域进入","command":{"producer_id":"bell-synthetic","source_event_id":"fixture-danger-zone","event_type":"danger-zone-entry","occurred_at":"2026-08-12T09:00:00Z","location":"北侧围墙","severity":"high","evidence_ref":"evidence://synthetic/danger-zone","attributes":{"object":"anonymous-person","zone":"north-wall"}}}

Bell/server/testdata/events/fixtures.go

@@ -0,0 +1,57 @@
+package events
+
+import (
+	"embed"
+	"encoding/json"
+	"fmt"
+	"io/fs"
+	"sort"
+
+	bellEvent "git.ilapage.cn/ila/yovision/Bell/server/app/event"
+)
+
+//go:embed *.json
+var files embed.FS
+
+type Fixture struct {
+	Name            string            `json:"name"`
+	Label           string            `json:"label"`
+	ValidationError string            `json:"validation_error,omitempty"`
+	Command         bellEvent.Command `json:"command"`
+}
+
+func All() ([]Fixture, error) {
+	entries, err := fs.ReadDir(files, ".")
+	if err != nil {
+		return nil, err
+	}
+	items := []Fixture{}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		data, err := files.ReadFile(entry.Name())
+		if err != nil {
+			return nil, err
+		}
+		var item Fixture
+		if err := json.Unmarshal(data, &item); err != nil {
+			return nil, fmt.Errorf("decode fixture %s: %w", entry.Name(), err)
+		}
+		items = append(items, item)
+	}
+	sort.Slice(items, func(i, j int) bool { return items[i].Name < items[j].Name })
+	return items, nil
+}
+func Find(name string) (Fixture, error) {
+	items, err := All()
+	if err != nil {
+		return Fixture{}, err
+	}
+	for _, item := range items {
+		if item.Name == name {
+			return item, nil
+		}
+	}
+	return Fixture{}, fmt.Errorf("unknown synthetic fixture %q", name)
+}

Bell/server/testdata/events/invalid-fields.json

@@ -0,0 +1 @@
+{"name":"invalid-fields","label":"字段无效（预期失败）","validation_error":"夹具用于验证字段拒绝","command":{"producer_id":"bell-synthetic","source_event_id":"fixture-invalid","event_type":"","occurred_at":"2026-08-12T09:02:00Z","location":"测试区域","severity":"unknown","attributes":{}}}

Bell/server/testdata/events/line-crossing.json

@@ -0,0 +1 @@
+{"name":"line-crossing","label":"方向越线","command":{"producer_id":"bell-synthetic","source_event_id":"fixture-line-crossing","event_type":"line-crossing","occurred_at":"2026-08-12T09:01:00Z","location":"宿舍楼东门","severity":"critical","evidence_ref":"evidence://synthetic/line-crossing","attributes":{"direction":"outside-to-inside","object":"anonymous-person"}}}

Bell/server/testdata/events/missing-evidence.json

@@ -0,0 +1 @@
+{"name":"missing-evidence","label":"证据缺失（预期失败）","validation_error":"此测试场景要求证据引用","command":{"producer_id":"bell-synthetic","source_event_id":"fixture-missing-evidence","event_type":"danger-zone-entry","occurred_at":"2026-08-12T09:03:00Z","location":"测试区域","severity":"high","attributes":{"requires_evidence":true}}}