feat: 段页式记忆流转、coldcontext 重命名与安全治理

记忆层：
- MemoryBlock 承载 FrameTS/PageSeq/PageKind/BlockRole/CallID
- coldcontext 归档与回填按完整页传递，工具调用参数和配对键不丢失
- 召回先估算总 token，超预算时按全局页相似度标记 inactive
- inactive 仅是 context 渲染期状态，不落盘、不进入 coldcontext，Prune 后重置
- Peek/确认/Remove 两阶段召回，失败保留冷上下文副本
- stablemem 记录 last_recalled_at，删块连带清理边

命名：
- internal/memory/document → internal/memory/coldcontext
- Doc/DocEvent/DocHit → ColdDoc/ColdEvent/ColdHit
- ContextToColdContext/RecentColdContexts/FindColdContexts
- 保留既有 JSON 标签、doc_ 文件前缀与 doc_count 状态键，兼容存量数据

安全治理：
- 工具策略门禁、安全配置、事件总线发布者身份与入站脱敏
- 声明式 SecurityAPI 与 QQ owner/guest profile
- 日志保留策略与相关 e2e/回归判据

验证：go build ./...、go vet ./...、go test ./...（62 包）；
生产副本 e2e：7013 块迁移后 ID/向量/指纹 0 变化、0 缺失。

internal/agent/core/plugins.go

@@ -59,10 +59,9 @@ func (a *Agent) autoReloadPlugins() {
 // 根本不是插件，靠规则永远猜不对。
 var builtinToolOwner = map[string]string{
 	// 记忆子系统（内核能力，不是插件）
-	"memory_recall": "core", "memory_commit": "core", "memory_merge": "core",
-	"memory_purge": "core", "memory_edit": "core", "memory_delete_entity": "core",
-	"memory_block_merge": "core", "memory_introspect": "core",
-	"memory_document_query": "core", "memory_document_commit": "core",
+	"stablemem_recall": "core", "stablemem_commit": "core", "stablemem_merge": "core",
+	"stablemem_purge": "core", "stablemem_edit": "core", "stablemem_delete_entity": "core",
+	"stablemem_block_merge": "core", "stablemem_introspect": "core",
 	// 知识库
 	"knowledge_search": "core", "knowledge_create": "core", "knowledge_list": "core",
 	"knowledge_delete": "core", "knowledge_import_dir": "core",