feat: config with agents rework

modules/home-manager/coding/agents/default.nix

@@ -0,0 +1,10 @@
+# Per-tool agent sub-modules
+# Each module handles rendering canonical agent.toml definitions
+# for a specific AI coding tool.
+{
+  imports = [
+    ./opencode.nix
+    ./claude-code.nix
+    ./pi.nix
+  ];
+}