Add Agent execution guidelines & trim AGENTS.md

Introduce a new detailed Agent handbook (docs/【协作规范】Agent工作入口与执行准则-2026-06-22.md) and refactor AGENTS.md to be an entry-only navigation page. Update documentation cross-references (docs/README.md, project-memory README, document-map, team-conventions, development-workflow, decision-log and project-overview) to point to the new file and clarify reading/order rules, submission/validation constraints, and SpacetimeDB/back-end wording. Also adjust image canvas generation placement rules in the frontend doc and apply related changes to image-editor hooks/tests (src/components/image-editor/*). Purpose: separate high-level entry rules from complex execution details to reduce startup cost for complex tasks and centralize execution practices in a single guideline document.

docs/project-memory/shared-memory/document-map.md

@@ -1,12 +1,13 @@
 # 文档地图与阅读索引
 
-更新时间：`2026-05-15`
+更新时间：`2026-06-22`
 
 ## 当前文档入口
 
 | 场景 | 优先阅读 |
 | --- | --- |
 | 建立项目背景 | `README.md`、`AGENTS.md`、`docs/project-memory/shared-memory/project-overview.md` |
+| Agent 复杂任务执行规则 | `AGENTS.md`、`docs/【协作规范】Agent工作入口与执行准则-2026-06-22.md` |
 | 找当前文档 | `docs/README.md` |
 | 产品、命名、UI、协作和废弃路线 | `docs/【项目基线】当前产品与工程约束-2026-05-15.md` |
 | 后端、DDD、API、SpacetimeDB schema 和表目录 | `docs/【后端架构】server-rs与SpacetimeDB数据契约-2026-05-15.md` |
@@ -22,9 +23,10 @@
 通用复杂任务：
 
 1. `AGENTS.md`
-2. `docs/project-memory/shared-memory/`
-3. `docs/README.md`
-4. 与任务匹配的当前融合文档
+2. `docs/【协作规范】Agent工作入口与执行准则-2026-06-22.md`
+3. `docs/project-memory/shared-memory/`
+4. `docs/README.md`
+5. 与任务匹配的当前融合文档
 
 后端 / 数据真相 / SpacetimeDB：
 
@@ -48,6 +50,7 @@
 ## 维护规则
 
 - 当前 `docs/` 只保留少量融合文档。
+- `AGENTS.md` 只保留最高优先级入口；Agent 执行细则优先沉到 `docs/【协作规范】Agent工作入口与执行准则-2026-06-22.md` 或对应专题文档。
 - 新增工程实现时，如果已有对应当前文档，必须同步更新。
 - 如果没有合适位置，新文档文件名必须使用 `【标签名】中文标题-YYYY-MM-DD.md`。
 - 阶段性流水账、一次性修复记录和已关闭实验不要再新增为长期文档。