fix: address final review — AAAI→EMNLP, chs→Video-Tree-TRM, D7 config boundary

- ARCHITECTURE.md: fix target conference AAAI→EMNLP
- subagent-driven-development SKILL.md: fix remaining chs env reference
- .env.example: remove EMBED_BACKEND/EMBED_MODEL (D7: belongs in YAML)
- config/default.yaml: clarify as research experiment config source

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/skills/subagent-driven-development/SKILL.md

@@ -161,7 +161,7 @@ Read the plan file once. Extract every task's full text and its surrounding cont
 
 Before spawning the first implementer subagent, ensure the knowledge graph is current so the implementer can consult it for structural context.
 
-**Prerequisite:** Graphify 已装进 `chs` 环境、且 `/graphify` skill 已项目局部安装（`.claude/skills/graphify/`）。首次知识图谱须由人类手动跑 `/graphify .`（全量混合：代码 tree-sitter + 文档 LLM 语义）。若 `graphify-out/graph.json` 不存在，则一次性提示人类先手动 `/graphify .`，本步降级为常规文件读取、不阻断流程。
+**Prerequisite:** Graphify 已装进 `Video-Tree-TRM` 环境、且 `/graphify` skill 已项目局部安装（`.claude/skills/graphify/`）。首次知识图谱须由人类手动跑 `/graphify .`（全量混合：代码 tree-sitter + 文档 LLM 语义）。若 `graphify-out/graph.json` 不存在，则一次性提示人类先手动 `/graphify .`，本步降级为常规文件读取、不阻断流程。
 
 **Run（控制器执行，增量合并刷新）:**