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/api/codec_chunkfast_bench_test.go

@@ -14,7 +14,7 @@ import (
 var benchChunks = map[string]string{
 	"content_zh":    `{"id":"chatcmpl-abc","object":"chat.completion.chunk","created":1727000000,"model":"deepseek-v4.1-flash","choices":[{"index":0,"delta":{"content":"这是一段来自真实流式响应的中文内容，用于测量解析开销。"},"finish_reason":null}]}`,
 	"content_ascii": `{"id":"chatcmpl-abc","choices":[{"index":0,"delta":{"content":"hello world this is a longer ascii content chunk"},"finish_reason":null}]}`,
-	"toolcall":      `{"id":"chatcmpl-abc","object":"chat.completion.chunk","created":1727000000,"model":"deepseek-v4.1-flash","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"id":"call_9a","type":"function","function":{"name":"memory_recall","arguments":"{\"query\":\"用户偏好\",\"limit\":20}"}}]},"finish_reason":null}]}`,
+	"toolcall":      `{"id":"chatcmpl-abc","object":"chat.completion.chunk","created":1727000000,"model":"deepseek-v4.1-flash","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"id":"call_9a","type":"function","function":{"name":"stablemem_recall","arguments":"{\"query\":\"用户偏好\",\"limit\":20}"}}]},"finish_reason":null}]}`,
 	"usage":         `{"id":"chatcmpl-abc","object":"chat.completion.chunk","created":1727000000,"model":"deepseek-v4.1-flash","choices":[{"index":0,"delta":{"content":""},"finish_reason":null}],"usage":{"prompt_tokens":3821,"completion_tokens":117,"total_tokens":3938,"prompt_cache_hit_tokens":3584,"prompt_cache_miss_tokens":237}}`,
 	"finish":        `{"id":"c","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}`,
 }