docs: split model source records and unify project instructions (#113)

* docs: split model sources and consolidate project instructions

* docs: normalize empty model navigation footer

docs/model-sources/providers/cohere/README.md

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+# Cohere：来源导航
+
+[总索引](../../README.md) · [官网证据与边界](SOURCES.md)
+
+本目录包含 10 个单模型文件、2 个单接入面文件。核验日期与状态来自迁移前记录。
+
+## 接入面
+
+- [compute/providers/cohere.json](access/providers--cohere.md)
+- [compute/model-specs/cohere.json](access/model-specs--cohere.md)
+
+## 模型
+
+- [`command-a-03-2025`](models/command-a-03-2025.md)
+- [`command-a-plus-05-2026`](models/command-a-plus-05-2026.md)
+- [`command-r7b-12-2024`](models/command-r7b-12-2024.md)
+- [`embed-v4.0`](models/embed-v4.0.md)
+- [`embed-v5.0-fast`](models/embed-v5.0-fast.md)
+- [`embed-v5.0-pro`](models/embed-v5.0-pro.md)
+- [`north-mini-code`](models/north-mini-code.md)
+- [`rerank-v3.5`](models/rerank-v3.5.md)
+- [`rerank-v4.0-fast`](models/rerank-v4.0-fast.md)
+- [`rerank-v4.0-pro`](models/rerank-v4.0-pro.md)