docs: 同步仓库文档到 v1.1.1，补媒体记忆与接口扩展规则

五处文档此前停在 v1.0.0，而 v1.1.0/v1.1.1 都已发布并在现网运行。
本轮补齐三层记忆的媒体架构、模型工具的媒体参数、通信面 method 数，
以及冻结解除后的替代约束。

## 中英双语 OVERVIEW.md

三层记忆段只写了 Context/Document/Graph 三层，而 v1.1.0 起图片/音频是
三层里的一类节点。补上媒体记忆的架构概要：CAS + 引用计数 GC + 标记格式
（描述文本才是持久语义记忆，blob 是可淘汰的缓存）+ 插件边界贯通。

## 中英双语 ARCHITECTURE.md

- 「记忆工具」表补 `memory_commit`/`doc_commit` 的 `media_digests` 与
  `sentence_text`（后者从未暴露给模型，而它是媒体绑定链的必经环节）
- 「三层记忆」段新增媒体记忆子节：CAS 设计表（寻址/完整性/写入原子性/引用/GC）、
  标记格式、可选性（`enabled=false` 时整条链路静默退化）
- 「三个通信面」从 51 改为 55 个 method，新增四个 media method 的说明
- 「SDK 四通道」代码示例补媒体注入三方法 + 与 SetToolBlocks 的区别

## plugin-interface-matrix.md

- 状态从「完成 v2」改「完成 v3」，v3 记录 v1.1.1 的接口扩展
- §二 A3 DocMemoryAPI 补 InsertWithMedia
- §二 A4 补三个媒体注入方法 + 为何不能搭 SetToolBlocks 的车
- §二 A5 补 MediaAttachment 类型 + Triple/Doc/TextEvent 的扩展字段
- §六「新获得的能力」补 SetToolBlocks 已落地、媒体入记忆、插件主动发起
  带媒体的对话
- §七 冻结检查点补第 5 条（冻结已解除，取代它的是 §九）
- 新增 §九「v1.1.x 的接口扩展规则」：冻结解除后的三条硬约束
  （只增不减签名不改 / 新增方法方向 / 模板接线六处失败链）+ 验证方式
  （存量插件 17/17、旧产物 4/4 建链、模板断言、压测 -race）

## 为何分立两笔 commit

前一笔（SDK 仓 README + 内核 README）改的是给**插件开发者**看的文本，
本笔改的是给**架构师与维护者**看的技术文档。受众与改动层次不同，
放在同一个 commit 会让追溯时看不出"文档在哪一层跟上了代码"。

assets/docs/en/OVERVIEW.md

@@ -25,6 +25,19 @@ The significance lies in clear responsibility boundaries: the kernel focuses on
 
 Three progressive layers — context, cold archive, long-term graph memory — form an information decay and consolidation pipeline from short-term to persistent storage.
 
+**Media Memory (since v1.1.0)** — Images and audio are not attachments; they are a kind of node in all three layers:
+- **Content-addressed store (CAS)**: addressed by digest, metadata in SQLite and blobs on disk, identical bytes
+  stored once. Every `Get` re-verifies the digest (silently returning corrupt data is worse than an error).
+- **Reference-counted GC**: `owner_kind/owner_id/digest` is the primary key; context events, documents and graph
+  sentences each hold their own references. **Referenced items are never deleted** — only unowned content past
+  `minAge` is reclaimed.
+- **The description text is the durable semantic memory**: what the vision model produced is written into
+  plain-text memory as a `[<mime> <short digest>] <description>` marker and participates in vector retrieval and
+  distillation; the blob is only a cache that capacity GC may evict. Months later "that purple-blue-red
+  three-band chart" is still findable — via the description, not the bytes.
+- **Reaches the plugin boundary since v1.1.1**: plugins read and write media through `InsertWithMedia` /
+  `InjectInputMedia`; the model attaches media via the `media_digests` argument of `memory_commit` / `doc_commit`.
+
 ## What It Actually Does
 
 Code is in the project root, implemented in Go.