chore: add opencode config, replace AGENT.md with AGENTS.md

AGENTS.md

@@ -1,7 +1,5 @@
 You are on a nix system. This rust project contains a `flake.nix`.
 
-To run any command `CMD` use the nix develop shell like this `nix develop --command bash -c 'CMD'`.
-
 If you don't know a crate or the current crate version, use the `cratedoc` extension to get the crate documentation.
 
 Read the file `README.md` for further information about this project.

CLAUDE.md

@@ -1 +0,0 @@
-AGENT.md

opencode.json

@@ -0,0 +1,9 @@
+{
+  "$schema": "https://opencode.ai/config.json",
+  "mcp": {
+    "cratedocs": {
+      "type": "remote",
+      "url": "http://127.0.0.1:3000/sse"
+    }
+  }
+}