docs: overhaul docs IA and multilingual navigation

docs/reference/README.md

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+# Reference Catalogs
+
+Structured reference index for commands, providers, channels, and config.
+
+## Core References
+
+- Commands by workflow: [../commands-reference.md](../commands-reference.md)
+- Provider IDs / aliases / env vars: [../providers-reference.md](../providers-reference.md)
+- Channel setup + allowlists: [../channels-reference.md](../channels-reference.md)
+- Config defaults and keys: [../config-reference.md](../config-reference.md)
+
+## Usage
+
+Use this collection when you need precise CLI/config details rather than step-by-step tutorials.