feat(opencode): install kepano/obsidian-skills into ~/.agents/skills

Add obsidian-skills as a flake input (flake = false) and map each
skill subdirectory into ~/.agents/skills/<skill>, alongside the
existing local skills. Updates flow through `nix flake update
obsidian-skills`.

modules/home/cli-apps/opencode/default.nix

@@ -1,6 +1,7 @@
 {
   lib,
   config,
+  inputs,
   ...
 }:
 let
@@ -8,6 +9,19 @@ let
   inherit (lib.metacfg) mkBoolOpt;
 
   cfg = config.metacfg.cli-apps.opencode;
+
+  obsidianSkills =
+    lib.mapAttrs'
+      (
+        name: _:
+        lib.nameValuePair ".agents/skills/${name}" {
+          source = "${inputs.obsidian-skills}/skills/${name}";
+          recursive = true;
+        }
+      )
+      (
+        lib.filterAttrs (_: type: type == "directory") (builtins.readDir "${inputs.obsidian-skills}/skills")
+      );
 in
 {
   options.metacfg.cli-apps.opencode = {
@@ -20,9 +34,12 @@ in
       recursive = true;
     };
 
-    home.file.".agents/skills" = {
-      source = ../../../../config/agents/skills;
-      recursive = true;
-    };
+    home.file = {
+      ".agents/skills" = {
+        source = ../../../../config/agents/skills;
+        recursive = true;
+      };
+    }
+    // obsidianSkills;
   };
 }