refactor(docs): reorganize docs by type and locale

docs/README.md

@@ -0,0 +1,21 @@
+# PicoClaw Documentation
+
+Documentation is organized by document type first and language second.
+
+## Sections
+
+- `project/`: project-level translated entry documents
+- `guides/`: setup and usage guides
+- `reference/`: reference material and configuration details
+- `operations/`: debugging and troubleshooting
+- `security/`: security-related documentation
+- `architecture/`: architecture and internal design notes
+- `channels/`: channel-specific integration guides
+- `design/`: design proposals and investigations
+- `migration/`: migration notes
+
+## Language Naming
+
+- English documents use the base filename, for example `configuration.md`
+- Translations use `.<locale>.md`, for example `configuration.zh.md`
+- Code-adjacent translated READMEs follow the same convention